[FIR] Check conflicting overloads via scopes

Scopes may return private symbols from
supertypes, they should not clash with
symbols from the current class.

For example, see:
`FirLightTreeBlackBoxCodegenWithIrFakeOverrideGeneratorTestGenerated.FakeOverride#testPrivateFakeOverrides1`

Lombok shouldn't generate functions if the
user has defined explicit ones.

In K1 generated functions are not really
added to the declared members scope.

^KT-61243 Fixed

compiler/testData/diagnostics/tests/suspendConflictingOverloads.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // ISSUE: KT-57100
 // WITH_STDLIB
 
@@ -10,5 +11,5 @@ interface C07I02{
 }
 
 class C07C01: C07I01, C07I02 {
-    <!CONFLICTING_OVERLOADS!>override fun some()<!> {}
+    override fun some() {}
 }