Change behavior of equals/hashCode on adapted function references

Function references are now equal if they refer to the same function,
and if the parameter/return type adaptation, which happens when a
reference is used where some function type is expected, is exactly the
same. This includes the number of expected positional parameters (which
can be affected by defaults/varargs), whether the coercion of vararg
parameter to Array type happened, and whether the coercion of return
type to Unit happened.

 #KT-37543 Fixed

compiler/testData/codegen/box/callableReference/equality/extensionReceiverVsDefault.kt

@@ -0,0 +1,20 @@
+// FILE: test.kt
+
+fun checkNotEqual(x: Any, y: Any) {
+    if (x == y || y == x) throw AssertionError("$x and $y should NOT be equal")
+}
+
+fun target(s: String = "") {}
+
+fun capture1(fn: String.() -> Unit): Any = fn
+fun capture2(fn: () -> Unit): Any = fn
+
+fun box(): String {
+    checkNotEqual(capture1(::target), capture2(::target))
+    checkNotEqual(capture1(::target), captureFromOtherFile())
+    return "OK"
+}
+
+// FILE: fromOtherFile.kt
+
+fun captureFromOtherFile(): Any = capture2(::target)