Add "Min API" setting (#69)

Changing min API can be useful when working with R8, when it changes the code for older APIs.

Example:
```kotlin
import java. lang. Thread
import android.os.Looper

fun test3() {
    Looper.getMainLooper().isCurrentThread()
}
```

DEX with min API 21 (R8 enabled):
```dex
class KotlinExplorerKt$$ExternalSyntheticApiModelOutline0
    void KotlinExplorerKt$$ExternalSyntheticApiModelOutline0.m(android.os.Looper)
        -- 2 instructions
        0000: invoke-virtual {v0}, Landroid/os/Looper;.isCurrentThread:()Z // method@0003
        0003: return-void

class KotlinExplorerKt
    void KotlinExplorerKt.test3()
        -- 4 instructions
        0000: invoke-static {}, Landroid/os/Looper;.getMainLooper:()Landroid/os/Looper; // method@0002
        0003: move-result-object v0
        0004: invoke-static {v0}, LKotlinExplorerKt$$ExternalSyntheticApiModelOutline0;.m:(Landroid/os/Looper;)V // method@0000
        0007: return-void
```

DEX with min API 26 (R8 enabled):
```dex
class KotlinExplorerKt
    void KotlinExplorerKt.test3()
        -- 4 instructions
        0000: invoke-static {}, Landroid/os/Looper;.getMainLooper:()Landroid/os/Looper; // method@0001
        0003: move-result-object v0
        0004: invoke-virtual {v0}, Landroid/os/Looper;.isCurrentThread:()Z // method@0002
        0007: return-void
```

src/jvmMain/kotlin/dev/romainguy/kotlin/explorer/Disassembly.kt

@@ -96,6 +96,7 @@ suspend fun buildAndDisassemble(
     toolPaths: ToolPaths,
     source: String,
     r8rules: String,
+    minApi: Int,
     instructionSets: Map<ISA, Boolean>,
     onByteCode: (CodeContent) -> Unit,
     onDex: (CodeContent) -> Unit,
@@ -150,7 +151,7 @@ suspend fun buildAndDisassemble(
                 launch(ui) { updater.advance("") }
             }
 
-            val dexCompiler = DexCompiler(toolPaths, directory, r8rules)
+            val dexCompiler = DexCompiler(toolPaths, directory, r8rules, minApi)
 
             val dex = dexCompiler.buildDex(optimize, keepEverything)
 

src/jvmMain/kotlin/dev/romainguy/kotlin/explorer/KotlinExplorer.kt

@@ -433,6 +433,7 @@ private fun FrameWindowScope.MainMenu(
                 explorerState.toolPaths,
                 sourceTextArea.text,
                 explorerState.r8Rules,
+                explorerState.minApi,
                 instructionSets,
                 onByteCodeUpdate,
                 onDexUpdate,

src/jvmMain/kotlin/dev/romainguy/kotlin/explorer/Settings.kt

@@ -39,6 +39,7 @@ fun Settings(
     val androidHome = rememberTextFieldState(state.androidHome)
     val kotlinHome = rememberTextFieldState(state.kotlinHome)
     val r8rules = rememberTextFieldState(state.r8Rules)
+    val minApi = rememberTextFieldState(state.minApi.toString())
     val indent = rememberTextFieldState(state.indent.toString())
     val lineNumberWidth = rememberTextFieldState(state.lineNumberWidth.toString())
     val decompileHiddenIsa = remember { mutableStateOf(state.decompileHiddenIsa) }
@@ -47,6 +48,7 @@ fun Settings(
             androidHome.text.toString(),
             kotlinHome.text.toString(),
             r8rules.text.toString(),
+            minApi.text.toString(),
             indent.text.toString(),
             lineNumberWidth.text.toString(),
             decompileHiddenIsa.value
@@ -61,6 +63,7 @@ fun Settings(
         IntSetting("Decompiled code indent: ", indent, minValue = 2)
         IntSetting("Line number column width: ", lineNumberWidth, minValue = 1)
         MultiLineStringSetting("R8 rules: ", r8rules)
+        IntSetting("Min API: ", minApi, minValue = 1)
         BooleanSetting("Decompile hidden instruction sets", decompileHiddenIsa)
         Spacer(modifier = Modifier.height(8.dp))
         Buttons(saveEnabled = toolPaths.isValid, onSaveClick, onDismissRequest)
@@ -87,13 +90,15 @@ private fun ExplorerState.saveState(
     androidHome: String,
     kotlinHome: String,
     r8Rules: String,
+    minApi: String,
     indent: String,
     lineNumberWidth: String,
     decompileHiddenIsa: Boolean,
 ) {
     this.androidHome = androidHome
     this.kotlinHome = kotlinHome
     this.r8Rules = r8Rules
+    this.minApi = minApi.toIntOrNull() ?: 21
     this.indent = indent.toIntOrNull() ?: 4
     this.lineNumberWidth = lineNumberWidth.toIntOrNull() ?: 4
     this.decompileHiddenIsa = decompileHiddenIsa

src/jvmMain/kotlin/dev/romainguy/kotlin/explorer/State.kt

@@ -30,6 +30,7 @@ private const val KotlinHome = "KOTLIN_HOME"
 private const val Optimize = "OPTIMIZE"
 private const val KeepEverything = "KEEP_EVERYTHING"
 private const val R8Rules = "R8_RULES"
+private const val MinApi = "MIN_API"
 private const val AutoBuildOnStartup = "AUTO_BUILD_ON_STARTUP"
 private const val Presentation = "PRESENTATION"
 private const val ShowLineNumbers = "SHOW_LINE_NUMBERS"
@@ -58,6 +59,7 @@ class ExplorerState {
     var optimize by BooleanState(Optimize, true)
     var keepEverything by BooleanState(KeepEverything, true)
     var r8Rules by StringState(R8Rules, "")
+    var minApi by IntState(MinApi, 21)
     var autoBuildOnStartup by BooleanState(AutoBuildOnStartup, false)
     var presentationMode by BooleanState(Presentation, false)
     var showLineNumbers by BooleanState(ShowLineNumbers, false)
@@ -80,8 +82,7 @@ class ExplorerState {
         toolPaths = createToolPaths()
     }
 
-    private fun createToolPaths() =
-        ToolPaths(directory, Path.of(androidHome.toString()), Path.of(kotlinHome.toString()))
+    private fun createToolPaths() = ToolPaths(directory, Path.of(androidHome), Path.of(kotlinHome))
 
     private inner class BooleanState(key: String, initialValue: Boolean) :
         SettingsState<Boolean>(key, initialValue, { toBoolean() })

src/jvmMain/kotlin/dev/romainguy/kotlin/explorer/build/DexCompiler.kt

@@ -23,7 +23,7 @@ import java.nio.file.Files
 import java.nio.file.Path
 import kotlin.io.path.*
 
-class DexCompiler(private val toolPaths: ToolPaths, private val outputDirectory: Path, private val r8rules: String) {
+class DexCompiler(private val toolPaths: ToolPaths, private val outputDirectory: Path, private val r8rules: String, private val minApi: Int) {
     suspend fun buildDex(optimize: Boolean, keepEverything: Boolean): ProcessResult {
         return process(*buildDexCommand(optimize, keepEverything), directory = outputDirectory)
     }
@@ -45,7 +45,7 @@ class DexCompiler(private val toolPaths: ToolPaths, private val outputDirectory:
             add(toolPaths.d8.toString())
             add(if (optimize) "com.android.tools.r8.R8" else "com.android.tools.r8.D8")
             add("--min-api")
-            add("21")
+            add(minApi.toString())
             if (optimize) {
                 add("--pg-conf")
                 add("rules.txt")