K2: Implement partially constrained lambda analysis (PCLA)

It's expected to partially mimic the behavior of what
previously was called builder inference, but with more clear contracts
(documentation is in progress, though)

See a lot of fixed issues in the later commits with test data,
especially [red-to-green]

^KT-59791 In Progress

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -8,7 +8,9 @@ package org.jetbrains.kotlin.types.model
 import org.jetbrains.kotlin.builtins.functions.FunctionTypeKind
 import org.jetbrains.kotlin.resolve.checkers.EmptyIntersectionTypeChecker
 import org.jetbrains.kotlin.resolve.checkers.EmptyIntersectionTypeInfo
-import org.jetbrains.kotlin.types.*
+import org.jetbrains.kotlin.types.AbstractTypeChecker
+import org.jetbrains.kotlin.types.TypeCheckerState
+import org.jetbrains.kotlin.types.Variance
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 
@@ -310,6 +312,9 @@ interface TypeSystemInferenceExtensionContext : TypeSystemContext, TypeSystemBui
      */
     fun KotlinTypeMarker.convertToNonRaw(): KotlinTypeMarker
 
+    @K2Only
+    fun createSubstitutionFromSubtypingStubTypesToTypeVariables(): TypeSubstitutorMarker
+
     fun createCapturedStarProjectionForSelfType(
         typeVariable: TypeVariableTypeConstructorMarker,
         typesForRecursiveTypeParameters: List<KotlinTypeMarker>,
@@ -588,3 +593,6 @@ fun requireOrDescribe(condition: Boolean, value: Any?) {
 
 @RequiresOptIn("This kinds of type is obsolete and should not be used until you really need it")
 annotation class ObsoleteTypeKind
+
+@RequiresOptIn
+annotation class K2Only

core/descriptors/src/org/jetbrains/kotlin/types/checker/ClassicTypeSystemContext.kt

@@ -622,6 +622,11 @@ interface ClassicTypeSystemContext : TypeSystemInferenceExtensionContext, TypeSy
         errorSupportedOnlyInTypeInference()
     }
 
+    @K2Only
+    override fun createSubstitutionFromSubtypingStubTypesToTypeVariables(): TypeSubstitutorMarker {
+        error("Only for K2")
+    }
+
     override fun TypeSubstitutorMarker.safeSubstitute(type: KotlinTypeMarker): KotlinTypeMarker {
         require(type is UnwrappedType, type::errorMessage)
         require(this is TypeSubstitutor, this::errorMessage)