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/codegen/boxWithStdlib/callableReference/function/overloadedFunVsVal.kt

@@ -0,0 +1,19 @@
+import kotlin.reflect.*
+import kotlin.test.assertEquals
+
+class A {
+    val x = 1
+    fun x(): String = "OK"
+}
+
+val f1: KProperty1<A, Int> = A::x
+val f2: (A) -> String = A::x
+
+fun box(): String {
+    val a = A()
+
+    assertEquals(1, f1.get(a))
+    assertEquals("OK", f2(a))
+
+    return "OK"
+}