RegExp accessor getters: throw TypeError on non-object this

[frostney]

Summary

RegExp.prototype accessor getters should throw TypeError for primitive this values (null, undefined, number, etc.).

Why

9 test262 this-val-invalid-obj tests fail across all flag getters.

Current behavior

Getters pass primitives through to IsRegExpValue which returns false, throwing a generic error.

Expected behavior

Calling the getter with a primitive this throws TypeError immediately per ES2026 §22.2.6.*.

Scope notes

• Source: Goccia.Builtins.GlobalRegExp.pas RequireRegExpThis
• Add explicit is-object check before the IsRegExpValue call