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/library/LoadIterable.fir.txt

@@ -1,6 +1,6 @@
 public abstract interface LoadIterable<T : R|kotlin/Any!|> : R|kotlin/Any| {
-    public abstract fun getIterable(): R|ft<kotlin/collections/MutableIterable<ft<T & Any, T?>>, kotlin/collections/Iterable<ft<T & Any, T?>>?>|
+    public abstract fun getIterable(): R|ft<kotlin/collections/MutableIterable<T!>, kotlin/collections/Iterable<T!>?>|
 
-    public abstract fun setIterable(Iterable: R|ft<kotlin/collections/MutableIterable<ft<T & Any, T?>>, kotlin/collections/Iterable<ft<T & Any, T?>>?>|): R|kotlin/Unit|
+    public abstract fun setIterable(Iterable: R|ft<kotlin/collections/MutableIterable<T!>, kotlin/collections/Iterable<T!>?>|): R|kotlin/Unit|
 
 }

compiler/testData/loadJava/compiledJava/library/LoadIterator.fir.txt

@@ -1,6 +1,6 @@
 public abstract interface LoadIterator<T : R|kotlin/Any!|> : R|kotlin/Any| {
-    public abstract fun getIterator(): R|ft<kotlin/collections/MutableIterator<ft<T & Any, T?>>, kotlin/collections/Iterator<ft<T & Any, T?>>?>|
+    public abstract fun getIterator(): R|ft<kotlin/collections/MutableIterator<T!>, kotlin/collections/Iterator<T!>?>|
 
-    public abstract fun setIterator(iterator: R|ft<kotlin/collections/MutableIterator<ft<T & Any, T?>>, kotlin/collections/Iterator<ft<T & Any, T?>>?>|): R|kotlin/Unit|
+    public abstract fun setIterator(iterator: R|ft<kotlin/collections/MutableIterator<T!>, kotlin/collections/Iterator<T!>?>|): R|kotlin/Unit|
 
 }

compiler/testData/loadJava/compiledJava/library/Max.fir.txt

@@ -1,5 +1,5 @@
 public open class Max : R|kotlin/Any| {
-    public open fun <T : R|kotlin/Any!|, R|ft<kotlin/Comparable<in ft<T & Any, T?>>, kotlin/Comparable<in ft<T & Any, T?>>?>|> max(coll: R|ft<kotlin/collections/MutableCollection<out ft<T & Any, T?>>, kotlin/collections/Collection<out ft<T & Any, T?>>?>|): R|ft<T & Any, T?>|
+    public open fun <T : R|kotlin/Any!|, R|ft<kotlin/Comparable<in T!>, kotlin/Comparable<in T!>?>|> max(coll: R|ft<kotlin/collections/MutableCollection<out T!>, kotlin/collections/Collection<out T!>?>|): R|T!|
 
     public constructor(): R|test/Max|