test: add new incremental case

This is similar to the old `llvm/shift_right_plus_left` case, which was
disabled by 1b1c78c. The case is not enabled on the LLVM backend, since
incremental compilation support for this backend is a work in progress
and is tracked by #21165. It passes on the x86_64-linux target with the
self-hosted backend.

Resolves: #12288

test/incremental/change_shift_op

@@ -0,0 +1,23 @@
+#target=x86_64-linux-selfhosted
+#target=x86_64-linux-cbe
+#target=x86_64-windows-cbe
+#update=initial version
+#file=main.zig
+pub fn main() !void {
+    try foo(0x1300);
+}
+fn foo(x: u16) !void {
+    try std.io.getStdOut().writer().print("0x{x}\n", .{x << 4});
+}
+const std = @import("std");
+#expect_stdout="0x3000\n"
+#update=change to right shift
+#file=main.zig
+pub fn main() !void {
+    try foo(0x1300);
+}
+fn foo(x: u16) !void {
+    try std.io.getStdOut().writer().print("0x{x}\n", .{x >> 4});
+}
+const std = @import("std");
+#expect_stdout="0x130\n"