Fix false positive for HasPlatformType with member extension on 'dynamic'

#KT-29812 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/SpecifyTypeExplicitlyIntention.kt

@@ -99,6 +99,7 @@ class SpecifyTypeExplicitlyIntention : SelfTargetingRangeIntention<KtCallableDec
             val callable = declaration.resolveToDescriptorIfAny() as? CallableDescriptor ?: return null
             if (publicAPIOnly && !callable.visibility.isPublicAPI) return null
             val type = callable.returnType ?: return null
+            if (type.isDynamic()) return null
             if (reportPlatformArguments) {
                 if (!type.isFlexibleRecursive()) return null
             } else {

idea/testData/inspections/hasPlatformType/extensionOnDynamic.kt

@@ -0,0 +1,3 @@
+class C {
+    operator fun dynamic.plus(x: Any?) = this
+}