Use TypeSubstitutor to get the substituted underlying type for inline

classes, instead of MemberScope.

The primary motivation was to fix issues around type-mapping for inline
classes in FIR, which uses wrapped descriptors that have empty
MemberScopes.

compiler/testData/codegen/box/inlineClasses/boundCallableReferencePassedToInlineFunction.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // WITH_RUNTIME
 
 inline class IcInt(val i: Int) {