IR: do not inherit IrFakeOverride* from IrFunction/IrProperty

This will help to reduce boilerplate after making the latter classes.

Without this change, IrFunctionCommonImpl would not be able to be a
class because it would introduce a diamond class hierarchy, and thus
that would require copying all its contents to IrFunctionImpl and
IrFakeOverrideFunctionImpl.

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrFactory.kt

@@ -189,7 +189,7 @@ object PersistentIrFactory : IrFactory {
         isDelegated: Boolean,
         isExternal: Boolean,
         isExpect: Boolean,
-    ): IrFakeOverrideProperty =
+    ): IrProperty =
         PersistentIrFakeOverrideProperty(
             startOffset, endOffset, origin, name, visibility, modality,
             isVar, isConst, isLateinit, isDelegated, isExternal, isExpect,

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrFunction.kt

@@ -133,10 +133,11 @@ internal class PersistentIrFakeOverrideFunction(
         get() = _symbol?.descriptor ?: WrappedSimpleFunctionDescriptor()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)
-    override fun acquireSymbol(symbol: IrSimpleFunctionSymbol) {
+    override fun acquireSymbol(symbol: IrSimpleFunctionSymbol): IrSimpleFunction {
         assert(_symbol == null) { "$this already has symbol _symbol" }
         _symbol = symbol
         symbol.bind(this)
         (symbol.descriptor as? WrappedSimpleFunctionDescriptor)?.bind(this)
+        return this
     }
 }

compiler/ir/ir.tree.persistent/src/org/jetbrains/kotlin/ir/declarations/persistent/PersistentIrProperty.kt

@@ -140,10 +140,11 @@ internal class PersistentIrFakeOverrideProperty(
         get() = _symbol?.descriptor ?: WrappedPropertyDescriptor()
 
     @OptIn(ObsoleteDescriptorBasedAPI::class)
-    override fun acquireSymbol(symbol: IrPropertySymbol) {
+    override fun acquireSymbol(symbol: IrPropertySymbol): IrProperty {
         assert(_symbol == null) { "$this already has symbol _symbol" }
         _symbol = symbol
         symbol.bind(this)
         (symbol.descriptor as? WrappedPropertyDescriptor)?.bind(this)
+        return this
     }
 }