feat(function): add constant functions

Author: unrevised6419

src/function.ts

@@ -3,3 +3,19 @@ export function noop() {}
 export function identity<T>(value: T): T {
 	return value;
 }
+
+export function falseFn() {
+	return false;
+}
+
+export function trueFn() {
+	return true;
+}
+
+export function nullFn() {
+	return null;
+}
+
+export function undefinedFn() {
+	return undefined;
+}