NI: Support forking inference with heuristics

Mostly, it only affects FIR

It partially allows to consider several variance of constraints like
A<Int> & A<T> <: A<X_var> that are mostly brought by smart casts

^KT-49542 Fixed
^KT-50489 Relates

compiler/fir/checkers/checkers-component-generator/src/org/jetbrains/kotlin/fir/checkers/generator/diagnostics/FirDiagnosticsList.kt

@@ -503,6 +503,10 @@ object DIAGNOSTICS_LIST : DiagnosticList("FirErrors") {
         val ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_ANNOTATION by deprecationError<KtExpression>(LanguageFeature.ProhibitAssigningSingleElementsToVarargsInNamedForm)
         val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_ANNOTATION by warning<KtExpression>()
         val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_FUNCTION by warning<KtExpression>()
+
+        val INFERENCE_UNSUCCESSFUL_FORK by error<PsiElement> {
+            parameter<String>("message")
+        }
     }
 
     val AMBIGUITY by object : DiagnosticGroup("Ambiguity") {

compiler/fir/checkers/gen/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrors.kt

@@ -341,6 +341,7 @@ object FirErrors {
     val ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_ANNOTATION by deprecationError0<KtExpression>(ProhibitAssigningSingleElementsToVarargsInNamedForm)
     val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_ANNOTATION by warning0<KtExpression>()
     val REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_FUNCTION by warning0<KtExpression>()
+    val INFERENCE_UNSUCCESSFUL_FORK by error1<PsiElement, String>()
 
     // Ambiguity
     val OVERLOAD_RESOLUTION_AMBIGUITY by error1<PsiElement, Collection<FirBasedSymbol<*>>>(SourceElementPositioningStrategies.REFERENCE_BY_QUALIFIED)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/FirErrorsDefaultMessages.kt

@@ -250,6 +250,7 @@ import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INCONSISTENT_TYPE
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INCORRECT_CHARACTER_LITERAL
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INC_DEC_SHOULD_NOT_RETURN_UNIT
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INFERENCE_ERROR
+import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INFERENCE_UNSUCCESSFUL_FORK
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INFIX_MODIFIER_REQUIRED
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INITIALIZATION_BEFORE_DECLARATION
 import org.jetbrains.kotlin.fir.analysis.diagnostics.FirErrors.INITIALIZER_REQUIRED_FOR_DESTRUCTURING_DECLARATION
@@ -928,6 +929,7 @@ object FirErrorsDefaultMessages : BaseDiagnosticRendererFactory() {
         )
         map.put(REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_ANNOTATION, "Redundant spread (*) operator")
         map.put(REDUNDANT_SPREAD_OPERATOR_IN_NAMED_FORM_IN_FUNCTION, "Redundant spread (*) operator")
+        map.put(INFERENCE_UNSUCCESSFUL_FORK, "Unsuccessful inference fork at position: {0}", TO_STRING)
 
         map.put(TYPE_MISMATCH, "Type mismatch: inferred type is {1} but {0} was expected", TO_STRING, TO_STRING, NOT_RENDERED)
         map.put(THROWABLE_TYPE_MISMATCH, "Throwable type mismatch: actual type is {0}", TO_STRING, NOT_RENDERED)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt

@@ -370,6 +370,12 @@ private fun ConstraintSystemError.toDiagnostic(
                 typeVariableName,
             )
         }
+        is NoSuccessfulFork -> {
+            FirErrors.INFERENCE_UNSUCCESSFUL_FORK.createOn(
+                source,
+                position.initialConstraint.asStringWithoutPosition(),
+            )
+        }
         else -> null
     }
 }