K2: Fix PCLA breaking change when using a bare type on a type variable

See the change at docs/fir/pcla.md and the kdoc
at `getAndSemiFixCurrentResultIfTypeVariable` for clarification

^KT-64840 Fixed

compiler/testData/diagnostics/tests/inference/builderInference/lambdaParameterForBareType.fir.kt

@@ -1,20 +0,0 @@
-// ISSUE: KT-64840 (K2/PCLA difference)
-class Controller<T> {
-    fun yield(t: T): Boolean = true
-}
-
-fun <S> generate(g: suspend Controller<S>.() -> Unit): S = TODO()
-
-interface A<F> {
-    val a: F?
-}
-
-interface B<G> : A<G>
-
-fun <X> predicate(x: X, c: Controller<in X>, p: (X) -> Boolean) {}
-
-fun main(a: A<*>) {
-    generate {
-        predicate(a, this) { it is <!NO_TYPE_ARGUMENTS_ON_RHS!>B<!> }
-    }.a
-}

compiler/testData/diagnostics/tests/inference/builderInference/lambdaParameterForBareType.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // ISSUE: KT-64840 (K2/PCLA difference)
 class Controller<T> {
     fun yield(t: T): Boolean = true

compiler/testData/diagnostics/tests/inference/builderInference/lambdaParameterForBareTypeAs.fir.kt

@@ -18,8 +18,8 @@ fun <X> withCallback(x: X, c: Controller<in X>, p: (X) -> Unit) {}
 fun main(a: A<String>) {
     val x = generate {
         withCallback(a, this) {
-            (it as <!NO_TYPE_ARGUMENTS_ON_RHS!>B<!>).<!UNRESOLVED_REFERENCE!>b<!>.length
-            it.<!UNRESOLVED_REFERENCE!>b<!>.length
+            (it as B).b.length
+            it.b.length
             it.a.length
         }
     }

compiler/testData/diagnostics/tests/inference/builderInference/lambdaParameterForBareTypeEarlyFixationAffectsBehavior.fir.kt

@@ -15,6 +15,8 @@ interface C : CommonSupertype
 fun <X> predicate(x: X, c: Controller<X>, p: (X) -> Unit) {}
 
 fun main(a: A<*>, c: C) {
+    // Without having `is` check
+    // This PCLA/BI call works in the same way both in K1 and K2
     val x1 = generate {
         predicate(a, this) { x ->
             // x is B
@@ -25,13 +27,19 @@ fun main(a: A<*>, c: C) {
 
     <!DEBUG_INFO_EXPRESSION_TYPE("CommonSupertype")!>x1<!>
 
+    // But introducing `is` on the expression of `Xv` type as LHS and a bare type on RHS
+    // Leads to an early fixation of Xv to the current result type (A<*>) and automatically it leads to Sv fixation, too
+    // This case works differently in K1 (BI) and in K2 (PCLA), but in both cases it's red code
+    // Without the last `yield` call, it would be even green in K2
     val x2 = generate {
         predicate(a, this) { x ->
-            x is <!NO_TYPE_ARGUMENTS_ON_RHS!>B<!>
+            x is B
         }
 
-        yield(c)
+        // For Sv we've got an EQUALITY constraint to A<*>
+        // Thus not allowing C type here
+        yield(<!ARGUMENT_TYPE_MISMATCH!>c<!>)
     }
 
-    <!DEBUG_INFO_EXPRESSION_TYPE("CommonSupertype")!>x2<!>
+    <!DEBUG_INFO_EXPRESSION_TYPE("A<*>")!>x2<!>
 }

compiler/testData/diagnostics/tests/inference/builderInference/lambdaParameterForBareTypeEarlyFixationAffectsBehavior.kt

@@ -15,6 +15,8 @@ interface C : CommonSupertype
 fun <X> predicate(x: X, c: Controller<X>, p: (X) -> Unit) {}
 
 fun main(a: A<*>, c: C) {
+    // Without having `is` check
+    // This PCLA/BI call works in the same way both in K1 and K2
     val x1 = generate {
         predicate(a, this) { x ->
             // x is B
@@ -25,11 +27,17 @@ fun main(a: A<*>, c: C) {
 
     <!DEBUG_INFO_EXPRESSION_TYPE("CommonSupertype")!>x1<!>
 
+    // But introducing `is` on the expression of `Xv` type as LHS and a bare type on RHS
+    // Leads to an early fixation of Xv to the current result type (A<*>) and automatically it leads to Sv fixation, too
+    // This case works differently in K1 (BI) and in K2 (PCLA), but in both cases it's red code
+    // Without the last `yield` call, it would be even green in K2
     val x2 = generate {
         predicate(a, this) { x ->
             <!USELESS_IS_CHECK!>x is <!NO_TYPE_ARGUMENTS_ON_RHS!>B<!><!>
         }
 
+        // For Sv we've got an EQUALITY constraint to A<*>
+        // Thus not allowing C type here
         yield(c)
     }