Don't refer self function in Fir2IrLazySimpleFunction.initialSignature

This commit prevents stack overflow in MethodSignatureMapper
#KT-49222 Fixed

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/lazy/Fir2IrLazySimpleFunction.kt

@@ -86,7 +86,7 @@ class Fir2IrLazySimpleFunction(
     }
 
     override val initialSignatureFunction: IrFunction? by lazy {
-        (fir.initialSignatureAttr as? FirFunction)?.symbol?.let { declarationStorage.getIrFunctionSymbol(it).owner }
+        (fir.initialSignatureAttr as? FirFunction)?.symbol?.let { declarationStorage.getIrFunctionSymbol(it).owner }?.takeIf { it !== this }
     }
 
     override val containerSource: DeserializedContainerSource?

compiler/testData/codegen/box/specialBuiltins/mapGetOrDefault.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // TARGET_BACKEND: JVM
 // JVM_TARGET: 1.8
 // WITH_RUNTIME