lang: core: Simplify list and map lookup default functions

examples/lang/lookup_default.mcl

@@ -0,0 +1,22 @@
+import "fmt"
+
+$some_list = ["l", "m", "n",]
+
+$some_map = {
+	"ottawa" => 6,
+	"toronto" => 7,
+	"montreal" => 8,
+	"vancouver" => 9,
+}
+
+print "letter" {
+	msg => fmt.printf("letter: %s", $some_list[13] || "j"),
+
+	Meta:autogroup => false,
+}
+
+print "city" {
+	msg => fmt.printf("city: %d", $some_map["montréal"] || 13),
+
+	Meta:autogroup => false,
+}