FIR: take expected type into account during inference

NB: this commit provokes some inference problems,
which are fixed by next commit about type inference for assignments

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/FirBodyResolveTransformer.kt

@@ -39,6 +39,7 @@ import org.jetbrains.kotlin.resolve.calls.NewCommonSuperTypeCalculator
 import org.jetbrains.kotlin.resolve.calls.components.InferenceSession
 import org.jetbrains.kotlin.resolve.calls.inference.buildAbstractResultingSubstitutor
 import org.jetbrains.kotlin.resolve.calls.inference.components.KotlinConstraintSystemCompleter
+import org.jetbrains.kotlin.resolve.calls.inference.model.SimpleConstraintSystemConstraintPosition
 import org.jetbrains.kotlin.resolve.calls.results.TypeSpecificityComparator
 import org.jetbrains.kotlin.types.model.*
 import org.jetbrains.kotlin.utils.addIfNotNull
@@ -602,6 +603,10 @@ open class FirBodyResolveTransformer(val session: FirSession, val implicitTypeOn
 
         val initialType = initialSubstitutor.substituteOrSelf(typeRef.type)
 
+        if (expectedTypeRef is FirResolvedTypeRef) {
+            candidate.system.addSubtypeConstraint(initialType, expectedTypeRef.type, SimpleConstraintSystemConstraintPosition)
+        }
+
         val completionMode = candidate.computeCompletionMode(inferenceComponents, expectedTypeRef, initialType)
         val completer = ConstraintSystemCompleter(inferenceComponents)
         val replacements = mutableMapOf<FirExpression, FirExpression>()

compiler/fir/resolve/testData/resolve/stdlib/hashSet.txt

@@ -1,5 +1,5 @@
 FILE: hashSet.kt
-    public final val a: R|kotlin/collections/MutableSet<kotlin/String>|? = R|java/util/HashSet.HashSet|<R|kotlin/Any|?>()
+    public final val a: R|kotlin/collections/MutableSet<kotlin/String>|? = R|java/util/HashSet.HashSet|<R|kotlin/String|>()
         public get(): R|kotlin/collections/MutableSet<kotlin/String>|?
     public final var b: R|kotlin/collections/MutableSet<kotlin/String>|? = Null(null)
         public get(): R|kotlin/collections/MutableSet<kotlin/String>|?