[FIR] Fix inference in presence of Unit expected type

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/FirCallCompleter.kt

@@ -31,6 +31,7 @@ import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.impl.ConeClassLikeTypeImpl
 import org.jetbrains.kotlin.fir.visitors.transformSingle
 import org.jetbrains.kotlin.name.Name
+import org.jetbrains.kotlin.resolve.calls.inference.addEqualityConstraintIfCompatible
 import org.jetbrains.kotlin.resolve.calls.inference.addSubtypeConstraintIfCompatible
 import org.jetbrains.kotlin.resolve.calls.inference.buildAbstractResultingSubstitutor
 import org.jetbrains.kotlin.resolve.calls.inference.components.ConstraintSystemCompletionMode
@@ -175,6 +176,9 @@ class FirCallCompleter(
                 system.addSubtypeConstraint(initialType, expectedType, expectedTypeConstraintPosition)
             }
             system.notFixedTypeVariables.isEmpty() -> return
+            expectedType.isUnit -> {
+                system.addEqualityConstraintIfCompatible(initialType, expectedType, expectedTypeConstraintPosition)
+            }
             else -> {
                 system.addSubtypeConstraintIfCompatible(initialType, expectedType, expectedTypeConstraintPosition)
             }

compiler/testData/diagnostics/tests/inference/coercionToUnit/coercionWithExpectedTypeAndBound.fir.kt

@@ -2,11 +2,11 @@
 fun <T : Number> materializeNumber(): T = TODO()
 
 fun a(): Unit = run {
-    <!NEW_INFERENCE_ERROR!>materializeNumber()<!>
+    <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>materializeNumber<!>()
 }
 
 fun b(): Unit = run {
     run {
-        <!NEW_INFERENCE_ERROR!>materializeNumber()<!>
+        <!NEW_INFERENCE_NO_INFORMATION_FOR_PARAMETER!>materializeNumber<!>()
     }
 }

compiler/testData/diagnostics/tests/inference/coercionToUnit/coerctionToUnitForATypeWithUpperBound.fir.kt

@@ -1,14 +0,0 @@
-// !DIAGNOSTICS: -UNUSED_PARAMETER
-
-interface Base
-class Foo : Base
-
-fun <T : Base> myRun(action: () -> T): T = action()
-
-fun foo(f: (Foo) -> Unit) {}
-
-fun main() {
-    foo { f: Foo ->
-        <!NEW_INFERENCE_ERROR!>myRun { f }<!>
-    }
-}

compiler/testData/diagnostics/tests/inference/coercionToUnit/coerctionToUnitForATypeWithUpperBound.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 // !DIAGNOSTICS: -UNUSED_PARAMETER
 
 interface Base