No override check in FirClassUseSiteScope, fix nasty substitution bug

This fixes MPP override test
(see mppFakeOverride in FirMultiModuleResolveTestGenerated)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirClassSubstitutionScope.kt

@@ -37,7 +37,7 @@ class FirClassSubstitutionScope(
     }
 
     private fun ConeKotlinType.substitute(): ConeKotlinType? {
-        if (this is ConeTypeParameterType) return substitution[this]
+        if (this is ConeTypeParameterType) return substitution[lookupTag]
 
         val newArguments by lazy { arrayOfNulls<ConeKotlinTypeProjection>(typeArguments.size) }
         var initialized = false

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirClassUseSiteScope.kt

@@ -72,7 +72,7 @@ class FirClassUseSiteScope(
         val self = (this as AbstractFirBasedSymbol<*>).fir as FirCallableMember
         val overriding = seen.firstOrNull {
             val member = (it as AbstractFirBasedSymbol<*>).fir as FirCallableMember
-            member.isOverride && self.modality != Modality.FINAL
+            self.modality != Modality.FINAL
                     && sameReceivers(member.receiverTypeRef, self.receiverTypeRef)
                     && similarFunctionsOrBothProperties(member, self)
         } // TODO: two or more overrides for one fun?

compiler/fir/resolve/testData/resolve/overrides/simple.kt

@@ -8,7 +8,7 @@ open class A {
 
 class B : A() {
     override fun foo(): B = this
-    fun bar(): B = this // Ambiguity, no override here
+    fun bar(): B = this // Ambiguity, no override here (really it's just "missing override" and no ambiguity)
     override fun buz(p: B): B = this //No override as B <!:> A
 
     fun test() {

compiler/fir/resolve/testData/resolve/overrides/simple.txt

@@ -32,7 +32,7 @@ FILE: simple.kt
 
         public final function test(): R|kotlin/Unit| {
             R|/B.foo|()
-            <Ambiguity: bar, [/B.bar, /A.bar]>#()
+            R|/B.bar|()
             <Ambiguity: buz, [/B.buz, /A.buz]>#()
         }
 

compiler/fir/resolve/testData/resolve/overrides/simpleFakeOverride.txt

@@ -15,7 +15,7 @@ FILE: simpleFakeOverride.kt
         public constructor(): super<R|A<Some>|>()
 
         public final function test(): R|kotlin/Unit| {
-            R|FakeOverride</A.foo: R|T|>|(<Unresolved name: Some>#())
+            R|FakeOverride</A.foo: R|Some|>|(<Unresolved name: Some>#())
         }
 
     }