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/coercionToUnitWithDefaults.kt

@@ -0,0 +1,34 @@
+// IGNORE_BACKEND: JVM_IR, 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")
+}
+
+fun target(x: Int, y: String = "", z: String = ""): Int = x
+
+fun captureNoDefaults(fn: (Int, String, String) -> Unit): Any = fn
+fun captureOneDefault(fn: (Int, String) -> Unit): Any = fn
+fun captureAllDefaults(fn: (Int) -> Unit): Any = fn
+
+fun box(): String {
+    checkEqual(captureNoDefaults(::target), captureNoDefaults(::target))
+    checkEqual(captureOneDefault(::target), captureOneDefault(::target))
+    checkEqual(captureAllDefaults(::target), captureAllDefaults(::target))
+    checkEqual(captureNoDefaults(::target), captureNoDefaultsFromOtherFile())
+
+    checkNotEqual(captureNoDefaults(::target), captureOneDefault(::target))
+    checkNotEqual(captureNoDefaults(::target), captureAllDefaults(::target))
+
+    return "OK"
+}
+
+// FILE: fromOtherFile.kt
+
+fun captureNoDefaultsFromOtherFile(): Any = captureNoDefaults(::target)