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

- Import aliasing symbol in file
- Missing function calls in conditional
- Missing return statement

Use an empty string instead of null for reseting styles

Fixes cases where styles value can no longer be null

For #81574

Adopt icon font in problems and peek error

Fixes #81887

Related xtermjs/xterm.js#291