Support "::foo" as a short-hand for "this::foo"

#KT-15667 Fixed

compiler/testData/diagnostics/tests/callableReference/function/innerConstructorFromClass.kt

@@ -1,12 +1,14 @@
 // !CHECK_TYPE
 // !DIAGNOSTICS: -UNUSED_EXPRESSION
+// !LANGUAGE: +CallableReferencesToClassMembersWithEmptyLHS
+
 import kotlin.reflect.KFunction1
 
 class A {
     inner class Inner
     
     fun main() {
-        ::<!CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS!>Inner<!>
+        ::Inner
         val y = A::Inner
 
         checkSubtype<KFunction1<A, Inner>>(y)

compiler/testData/diagnostics/tests/callableReference/function/innerConstructorFromExtension.kt

@@ -1,5 +1,7 @@
 // !CHECK_TYPE
 // !DIAGNOSTICS: -UNUSED_EXPRESSION
+// !LANGUAGE: +CallableReferencesToClassMembersWithEmptyLHS
+
 import kotlin.reflect.KFunction1
 
 class A {
@@ -7,7 +9,7 @@ class A {
 }
     
 fun A.main() {
-    ::<!CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS!>Inner<!>
+    ::Inner
     val y = A::Inner
 
     checkSubtype<KFunction1<A, A.Inner>>(y)

compiler/testData/diagnostics/tests/callableReference/function/noAmbiguityMemberVsTopLevel.kt

@@ -1,24 +1,31 @@
 // !CHECK_TYPE
+// !LANGUAGE: +CallableReferencesToClassMembersWithEmptyLHS
 
 import kotlin.reflect.KFunction0
 
-fun explicitlyExpectFunction0(f: () -> Unit) = f
-fun explicitlyExpectFunction1(f: (A) -> Unit) = f
+fun expectFunction0Unit(f: () -> Unit) = f
+fun expectFunction0String(f: () -> String) = f
+fun expectFunction1Unit(f: (A) -> Unit) = f
+fun expectFunction1String(f: (A) -> String) = f
 
-fun foo() {}
+fun foo(): String = ""
 
 class A {
     fun foo() {}
     
     fun main() {
-        val x = ::<!CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS!>foo<!>
+        val x = ::foo
 
         checkSubtype<KFunction0<Unit>>(x)
 
-        explicitlyExpectFunction0(x)
-        explicitlyExpectFunction1(<!TYPE_MISMATCH!>x<!>)
+        expectFunction0Unit(x)
+        expectFunction0String(<!TYPE_MISMATCH!>x<!>)
+        expectFunction1Unit(<!TYPE_MISMATCH!>x<!>)
+        expectFunction1String(<!TYPE_MISMATCH!>x<!>)
 
-        explicitlyExpectFunction0(::<!CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS!>foo<!>)
-        explicitlyExpectFunction1(<!TYPE_MISMATCH!>::<!CALLABLE_REFERENCE_TO_MEMBER_OR_EXTENSION_WITH_EMPTY_LHS!>foo<!><!>)
+        expectFunction0Unit(::foo)
+        expectFunction0String(::foo)
+        expectFunction1Unit(<!TYPE_MISMATCH!>::foo<!>)
+        expectFunction1String(<!TYPE_MISMATCH!>::foo<!>)
     }
 }

compiler/testData/diagnostics/tests/callableReference/function/noAmbiguityMemberVsTopLevel.txt

@@ -1,8 +1,10 @@
 package
 
-public fun explicitlyExpectFunction0(/*0*/ f: () -> kotlin.Unit): () -> kotlin.Unit
-public fun explicitlyExpectFunction1(/*0*/ f: (A) -> kotlin.Unit): (A) -> kotlin.Unit
-public fun foo(): kotlin.Unit
+public fun expectFunction0String(/*0*/ f: () -> kotlin.String): () -> kotlin.String
+public fun expectFunction0Unit(/*0*/ f: () -> kotlin.Unit): () -> kotlin.Unit
+public fun expectFunction1String(/*0*/ f: (A) -> kotlin.String): (A) -> kotlin.String
+public fun expectFunction1Unit(/*0*/ f: (A) -> kotlin.Unit): (A) -> kotlin.Unit
+public fun foo(): kotlin.String
 
 public final class A {
     public constructor A()