[FIR] Implement TYPE_VARIANCE_CONFLICT, TYPE_VARIANCE_CONFLICT_IN_EXPANDED_TYPE diagnostics, fix tests

compiler/testData/diagnostics/tests/generics/innerClasses/innerVariance.fir.kt

@@ -1,14 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-class Outer<out E, in F> {
-    inner class Inner {
-        fun unsafe1(x: E) {}
-        fun unsafe2(x: Collection<E?>) {}
-        fun unsafe3(): F? = null
-        fun unsafe4(): Collection<F>? = null
-    }
-
-    // Should be errors
-    // Refinement of variance checker is needed
-    fun foo(x: Inner) {}
-    fun bar(): Inner? = null
-}

compiler/testData/diagnostics/tests/generics/innerClasses/innerVariance.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 class Outer<out E, in F> {
     inner class Inner {