Prevent extracting hidden functions

I'm not sure how these looked in 1.6 and below yet, but in 1.7 they appear with visibility = public, but a descriptor field set to indicate they have a name clash with a 'real' function.

Author: smowton

java/kotlin-extractor/src/main/kotlin/KotlinFileExtractor.kt

@@ -86,6 +86,7 @@ open class KotlinFileExtractor(
         }
     }
 
+    @OptIn(ObsoleteDescriptorBasedAPI::class)
     private fun isFake(d: IrDeclarationWithVisibility): Boolean {
         val visibility = d.visibility
         if (visibility is DelegatedDescriptorVisibility && visibility.delegate == Visibilities.InvisibleFake) {
@@ -94,6 +95,9 @@ open class KotlinFileExtractor(
         if (d.isFakeOverride) {
             return true
         }
+        if ((d as? IrFunction)?.descriptor?.isHiddenToOvercomeSignatureClash == true) {
+            return true
+        }
         return false
     }