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/simpleEquality.kt

@@ -0,0 +1,47 @@
+// IGNORE_BACKEND: JS, JS_IR, NATIVE
+// IGNORE_BACKEND_FIR: JVM_IR
+// FILE: test.kt
+
+fun checkEqual(x: Any, y: Any) {
+    if (x != y || y != x) throw AssertionError("$x and $y should be equal")
+    if (x.hashCode() != y.hashCode()) throw AssertionError("$x and $y should have the same hash code")
+}
+
+fun checkNotEqual(x: Any, y: Any) {
+    if (x == y || y == x) throw AssertionError("$x and $y should NOT be equal")
+}
+
+class V {
+    val memberVal: String = ""
+    fun memberFun(): String = ""
+}
+
+val topLevelVar: String = ""
+fun topLevelFun(): String = ""
+
+fun box(): String {
+    val v0 = V()
+    val v1 = V()
+
+    checkEqual(::topLevelFun, ::topLevelFun)
+    checkEqual(::topLevelFun, referenceTopLevelFunFromOtherFile())
+    checkEqual(::topLevelVar, ::topLevelVar)
+    checkEqual(::topLevelVar, referenceTopLevelVarFromOtherFile())
+
+    checkEqual(V::memberFun, V::memberFun)
+    checkEqual(v0::memberFun, v0::memberFun)
+    checkEqual(V::memberVal, V::memberVal)
+    checkEqual(v0::memberVal, v0::memberVal)
+
+    checkNotEqual(v0::memberFun, V::memberFun)
+    checkNotEqual(v0::memberVal, V::memberVal)
+    checkNotEqual(v0::memberFun, v1::memberFun)
+    checkNotEqual(v0::memberVal, v1::memberVal)
+
+    return "OK"
+}
+
+// FILE: fromOtherFile.kt
+
+fun referenceTopLevelFunFromOtherFile() = ::topLevelFun
+fun referenceTopLevelVarFromOtherFile() = ::topLevelVar