Support bound references to objects and companion objects

Tweak member extension detection a little bit to prohibit extensions imported
from objects (they don't have one of the receiver parameters)

compiler/testData/diagnostics/tests/callableReference/bound/object.txt

@@ -0,0 +1,12 @@
+package
+
+public fun test(): kotlin.Unit
+
+public object Obj {
+    private constructor Obj()
+    public final val bar: kotlin.Int = 2
+    public open override /*1*/ /*fake_override*/ fun equals(/*0*/ other: kotlin.Any?): kotlin.Boolean
+    public 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
+}