add kdoc for findChildByTypeRecursively and endOffset

ktlint-rule-engine-core/src/main/kotlin/com/pinterest/ktlint/rule/engine/core/api/ASTNodeExtension.kt

@@ -571,9 +571,16 @@ public fun ASTNode.remove() {
     treeParent.removeChild(this)
 }
 
+/**
+ * Searches the receiver [ASTNode] recursively, returning the first child with type [elementType]. If none are found, returns [null].
+ * If [includeSelf] is [true], includes the receiver in the search. The receiver would then be the first element searched, so it is guaranteed to be returned if it has type [elementType].
+ */
 public fun ASTNode.findChildByTypeRecursively(
     elementType: IElementType,
     includeSelf: Boolean,
 ): ASTNode? = recursiveChildren(includeSelf).firstOrNull { it.elementType == elementType }
 
+/**
+ * Returns the end offset of the text of this [ASTNode]
+ */
 public fun ASTNode.endOffset(): Int = textRange.endOffset