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/testData/loadJava/compiledJava/constructor/ConstructorGenericDeep.fir.txt

@@ -1,4 +1,4 @@
 public open class ConstructorGenericDeep : R|kotlin/Any| {
-    public constructor<P : R|kotlin/Any!|>(cl: R|ft<java/lang/Class<ft<P & Any, P?>>, java/lang/Class<ft<P & Any, P?>>?>|): R|test/ConstructorGenericDeep|
+    public constructor<P : R|kotlin/Any!|>(cl: R|ft<java/lang/Class<P!>, java/lang/Class<P!>?>|): R|test/ConstructorGenericDeep|
 
 }

compiler/testData/loadJava/compiledJava/constructor/ConstructorGenericSimple.fir.txt

@@ -1,4 +1,4 @@
 public open class ConstructorGenericSimple : R|kotlin/Any| {
-    public constructor<P : R|kotlin/Any!|>(p: R|ft<P & Any, P?>|): R|test/ConstructorGenericSimple|
+    public constructor<P : R|kotlin/Any!|>(p: R|P!|): R|test/ConstructorGenericSimple|
 
 }

compiler/testData/loadJava/compiledJava/constructor/ConstructorGenericUpperBound.fir.txt

@@ -1,4 +1,4 @@
 public open class ConstructorGenericUpperBound : R|kotlin/Any| {
-    public constructor<P : R|java/util/RandomAccess!|>(p: R|ft<P & Any, P?>|): R|test/ConstructorGenericUpperBound|
+    public constructor<P : R|java/util/RandomAccess!|>(p: R|P!|): R|test/ConstructorGenericUpperBound|
 
 }