K2 KMP: Don't create invalid ConeSubstitutor when type parameters size doesn't match

When type parameters size doesn't match, it's better to pass `null`
instead of a parentSubstitutor. Before this commit we were creating an
invalid substitutor. Who knows what can go wrong because of that further
along the execution

Related issue: KT-54827
Related test: compiler/testData/diagnostics/tests/multiplatform/kt54827.kt
Review: https://jetbrains.team/p/kt/reviews/12279/files

Motivation for the commit: There is no user report or anything. It's not
known whether these invalid substitutors were causing problems. I just
noticed this problem while doing substitutor API refactoring (see the
next commit).

Note: `ExpectedActualResolver.matchActualCallableAgainstPotentialExpects`
has the same problem. But since it's K1 I won't touch it

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/mpp/FirExpectActualResolver.kt

@@ -44,15 +44,16 @@ object FirExpectActualResolver {
                                 ?.fullyExpandedClass(useSiteSession)
 
                             val expectTypeParameters = expectContainingClass?.typeParameterSymbols.orEmpty()
-                            val actualTypeParameters = actualContainingClass
-                                ?.typeParameterSymbols
-                                .orEmpty()
+                            val actualTypeParameters = actualContainingClass?.typeParameterSymbols.orEmpty()
 
-                            parentSubstitutor = createExpectActualTypeParameterSubstitutor(
-                                expectTypeParameters,
-                                actualTypeParameters,
-                                useSiteSession,
-                            )
+                            parentSubstitutor = when (expectTypeParameters.size == actualTypeParameters.size) {
+                                true -> createExpectActualTypeParameterSubstitutor(
+                                    expectTypeParameters,
+                                    actualTypeParameters,
+                                    useSiteSession,
+                                )
+                                false -> null
+                            }
 
                             when (actualSymbol) {
                                 is FirConstructorSymbol -> expectContainingClass?.getConstructors(scopeSession)