Add testcase for finalizer rescue on call unwind

This is trying to reproduce an issue found in Frida but seems to have no
issues with valgrind.

tests/api/test-dev-finalizer-rescue-unwind.c

@@ -0,0 +1,72 @@
+/*
+ *  Test finalizer rescue when the value being finalized/rescued becomes
+ *  unreachable as part of call handling unwind.
+ */
+
+/*===
+*** test_1 (duk_safe_call)
+calling
+finalizer, rescuing object {"name":"my object"}
+returned
+calling
+finalizer, rescuing object {"name":"my object"}
+returned
+final top: 0
+==> rc=0, result='undefined'
+finalizer, rescuing object {"name":"my object"}
+===*/
+
+static duk_ret_t my_func(duk_context *ctx) {
+	(void) ctx;
+	return 0;
+}
+
+static duk_ret_t test_1(duk_context *ctx) {
+	duk_eval_string_noresult(ctx,
+		"this.myFinalizer = function myfin(o) {\n"
+		"    print('finalizer, rescuing object', JSON.stringify(o));\n"
+		"    var global = new Function('return this')();\n"
+		"    global.rescued = o;\n"
+		"}\n"
+	);
+
+	/* First call; object gets finalized when call returns and call
+	 * handling does a duk_set_top() call.  The object is rescued and
+	 * later reused.
+	 */
+	duk_push_c_function(ctx, my_func, 3 /*nargs*/);
+	duk_push_null(ctx);
+	duk_eval_string(ctx,
+		"(function () {\n"
+		"    var res = { name: 'my object' };\n"
+		"    Duktape.fin(res, myFinalizer);\n"
+		"    return res;\n"
+		"})()\n");
+	duk_push_null(ctx);
+	printf("calling\n");
+	duk_call(ctx, 3);
+	printf("returned\n");
+	duk_pop(ctx);
+
+	/* Object is reused for another call, and rescued again. */
+	duk_push_c_function(ctx, my_func, 3 /*nargs*/);
+	duk_push_null(ctx);
+	duk_eval_string(ctx, "rescued");
+	duk_eval_string_noresult(ctx, "rescued = null;");
+	duk_push_null(ctx);
+	printf("calling\n");
+	duk_call(ctx, 3);
+	printf("returned\n");
+	duk_pop(ctx);
+
+	printf("final top: %ld\n", (long) duk_get_top(ctx));
+	return 0;
+}
+
+void test(duk_context *ctx) {
+	TEST_SAFE_CALL(test_1);
+
+	/* When we return the object is finalized once more as part of
+	 * heap destruction but no longer rescued.
+	 */
+}