FIR IDE: specify behaviour of HL API getOverriddenSymbols

- Split it into two functions getAllOverriddenSymbols and getDirectlyOverriddenSymbols
- Implement tests for getOverriddenSymbols
- temporary mute inheritance.kt light classes test

compiler/testData/asJava/ultraLightClasses/inheritance.kt

@@ -29,5 +29,3 @@ private class Private {
     override val overridesNothing: Boolean
         get() = false
 }
-
-// FIR_COMPARISON