Support overload ambiguity resolution for callable references by expected type.

Resolve callable references taking into account expected callable types.

This affects call resolution procedure (resolve 'foo' in for 'foo(::bar)') similar to the approach used for function literals:

* During "shape arguments" phase of call resolution, callable references are resolved in independent context without expected type. If the callable reference is ambiguous, its shape type is a function placeholder type without parameter types and return type information. Otherwise, it is a reflection type for the resolved function or property. Upper-level call is resolved without taking into account ambiguous callable references.

* During "complete call" phase of call resolution, resolve callable reference arguments to actual descriptors (if possible), and update constraint system for the given call accordingly.

 #KT-6982 Fixed
 #KT-5780 Fixed

compiler/testData/diagnostics/tests/callableReference/resolve/withExtFun.txt

@@ -0,0 +1,25 @@
+package
+
+internal val userOfX0: kotlin.Unit
+internal val x0: kotlin.reflect.KFunction1<A, kotlin.Unit>
+internal val x1: (A) -> kotlin.Unit
+internal val x2: kotlin.reflect.KProperty1<A, kotlin.Int>
+internal val x3: kotlin.reflect.KProperty1<A, kotlin.Int>
+internal val x4: (A) -> kotlin.String
+internal val y0: kotlin.reflect.KFunction1<A, kotlin.Unit>
+internal val y1: (A) -> kotlin.Unit
+internal val y2: kotlin.reflect.KProperty1<A, kotlin.Int>
+internal val y3: kotlin.reflect.KProperty1<A, kotlin.Int>
+internal fun </*0*/ T> ofType(/*0*/ x: T): T
+internal fun A.foo(): kotlin.String
+
+internal final class A {
+    public constructor A()
+    internal final val bar: kotlin.Int = 0
+    internal final val foo: kotlin.Int = 0
+    internal final fun bar(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    internal final fun foo(): kotlin.Unit
+    public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
+    public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
+}