LibJS: Implement the Number::remainder AO using fmod

The ECMA verbiage for modulus is the mathematical definition implemented
by fmod, so let's just use that rather than trying to reimplement all
the edge cases.

Userland/Libraries/LibJS/Tests/operators/modulo-basic.js

@@ -23,6 +23,7 @@ test("basic functionality", () => {
     expect(1 % -0).toBeNaN();
     expect(0 % 5).toBe(0);
     expect(-0 % 5).toBe(-0);
+    expect((-1) % -1).toBe(-0);
 
     // test262 examples
     expect(1 % null).toBeNaN();