K2: repeat K1 representation for flexible type parameters

This commit changes the behavior of KT-59138 effectively declining it in 2.0.
However, we plan to implement KT-59138 behavior under a feature
flag in 2.0 (see KT-66447), and switch this feature on version 2.x.

Also, this commit implements the LC resolution about postponing
KT-57014 change. We don't have KT-57014 described behavior in 2.0 anymore.
However, we plan to implement a deprecation warning here, see KT-65578.

After this commit, 6 diagnostic tests become incorrectly broken:
- 5 tests from PurelyImplementedCollection group
- a test platformTypes/nullableTypeArgument.kt

This commit also breaks currently fixed-in-k2 KT-50134
(it is fixed again in the following commits),
as well as KT-58933 (it will remain not fixed till we enable KT-59138
behavior again).

#KT-65596 In Progress
#KT-57014 In Progress
#KT-58933 Submitted

compiler/fir/analysis-tests/testData/resolve/inference/javaCollector.kt

@@ -6,12 +6,12 @@ import java.util.stream.Collectors
 
 fun foo(){
     listOf("").stream().collect(
-        Collectors.groupingBy(
+        <!ARGUMENT_TYPE_MISMATCH, NEW_INFERENCE_ERROR!>Collectors.groupingBy(
             { it },
             Collectors.collectingAndThen(
                 Collectors.counting<String>(),
                 Long::toInt
             )
-        )
+        )<!>
     )
 }