Render Octicons in CodeLens

fixes #72503

This reverts commit a8a448d1.

#78168Ï

#78168

Fixes #81780

Fixes #81783

This code was added to workaround bug in electron. It looks like it has since been fixed

Readonly helps out with TS's type guards and is also a good best practice. Specifically, readonly strings/numbers have their literal type instead of a generic `string` | `number` type, which can help catch dead code and some common programming mistakes

- Also switches a few places that re-implemented Disposable with calls to `_register` instead

See issue #81878

Prefer using these predicates as they are shorter and make the code easier to understand