Implement processSlotAttribute method (#2511)

There is some duplicated code to process attributes that can
be overridden by slots. In addition, not every attribute that can be
overridden with slots are processed with the 
hasSlotOverridingAttribute method. As such, there will be no
warning in the logger when these attributes are overridden.

Let's put this duplicated code into a method and call it for every
attribute that can be overridden by a slot.

packages/core/src/html/MdAttributeRenderer.ts

@@ -75,10 +75,23 @@ export class MdAttributeRenderer {
     return hasAttribute;
   }
 
-  processPopoverAttributes(node: MbNode) {
-    if (!this.hasSlotOverridingAttribute(node, 'header')) {
-      this.processAttributeWithoutOverride(node, 'header', true);
+  /**
+   * Checks if there is a pre-existing slot for the attribute.
+   * If there is a slot, it deletes the attribute and logs a warning.
+   * If there is no slot, it processes the markdown attribute.
+   * @param node Element to process
+   * @param attribute Attribute name to process
+   * @param isInline Whether to process the attribute with only inline markdown-it rules
+   * @param slotName Name attribute of the <slot> element to insert, which defaults to the attribute name
+   */
+  processSlotAttribute(node: MbNode, attribute: string, isInline: boolean, slotName = attribute) {
+    if (!this.hasSlotOverridingAttribute(node, attribute, slotName)) {
+      this.processAttributeWithoutOverride(node, attribute, isInline, slotName);
     }
+  }
+
+  processPopoverAttributes(node: MbNode) {
+    this.processSlotAttribute(node, 'header', true);
 
     // Warn if there is a content slot overriding the attributes 'content' or 'src'
     const hasSlotAndContentAttribute = this.hasSlotOverridingAttribute(node, 'content', 'content');
@@ -96,69 +109,63 @@ export class MdAttributeRenderer {
   }
 
   processTooltip(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'content', true);
+    this.processSlotAttribute(node, 'content', true);
   }
 
   processModalAttributes(node: MbNode) {
-    if (!this.hasSlotOverridingAttribute(node, 'header')) {
-      this.processAttributeWithoutOverride(node, 'header', true);
-    }
+    this.processSlotAttribute(node, 'header', true);
   }
 
   /*
    * Panels
    */
 
   processPanelAttributes(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'alt', false, '_alt');
-    if (!this.hasSlotOverridingAttribute(node, 'header')) {
-      this.processAttributeWithoutOverride(node, 'header', false);
-    }
+    this.processSlotAttribute(node, 'alt', false, '_alt');
+    this.processSlotAttribute(node, 'header', false);
   }
 
   /*
    * Questions, QOption, and Quizzes
    */
 
   processQuestion(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'header', false);
-    this.processAttributeWithoutOverride(node, 'hint', false);
-    this.processAttributeWithoutOverride(node, 'answer', false);
+    this.processSlotAttribute(node, 'header', false);
+    this.processSlotAttribute(node, 'hint', false);
+    this.processSlotAttribute(node, 'answer', false);
   }
 
   processQOption(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'reason', false);
+    this.processSlotAttribute(node, 'reason', false);
   }
 
   processQuiz(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'intro', false);
+    this.processSlotAttribute(node, 'intro', false);
   }
 
   /*
    * Tabs
    */
 
   processTabAttributes(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'header', true);
+    this.processSlotAttribute(node, 'header', true);
   }
 
   /*
    * Boxes
    */
 
   processBoxAttributes(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'icon', true);
-    this.processAttributeWithoutOverride(node, 'header', false);
+    this.processSlotAttribute(node, 'icon', true);
+    this.processSlotAttribute(node, 'header', false);
   }
 
   /*
    * Dropdowns
    */
 
   processDropdownAttributes(node: MbNode) {
-    if (!this.hasSlotOverridingAttribute(node, 'header')) {
-      this.processAttributeWithoutOverride(node, 'header', true);
-    }
+    this.processSlotAttribute(node, 'header', true);
   }
 
   /**
@@ -186,12 +193,12 @@ export class MdAttributeRenderer {
   }
 
   processScrollTopButtonAttributes(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'icon', true);
+    this.processSlotAttribute(node, 'icon', true);
   }
 
   processAnnotationPointAttributes(node: MbNode) {
-    this.processAttributeWithoutOverride(node, 'content', false);
-    this.processAttributeWithoutOverride(node, 'header', false);
-    this.processAttributeWithoutOverride(node, 'label', false);
+    this.processSlotAttribute(node, 'content', false);
+    this.processSlotAttribute(node, 'header', false);
+    this.processSlotAttribute(node, 'label', false);
   }
 }