[NI] Support fixation to subtype in completion mode calculator

Allow full compltion mode for return type depending on type parameters in
contravariant position only if they have proper equality constraint.

compiler/testData/diagnostics/tests/inference/completion/basic.fir.kt

@@ -57,7 +57,6 @@ fun test7(cls: Cls) {
 }
 
 fun test8(cls: Cls) {
-    // TODO
     id(
         wrapIn(cls)
     )