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/withVararg.kt

@@ -0,0 +1,10 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+fun foo(vararg ii: Int) {}
+fun foo(vararg ss: String) {}
+fun foo(i: Int) {}
+
+val fn1: (Int) -> Unit = ::foo
+val fn2: (IntArray) -> Unit = ::foo
+val fn3: (Int, Int) -> Unit = <!TYPE_MISMATCH!>::foo<!>
+val fn4: (Array<String>) -> Unit = ::foo