- 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

and handle flipped highlight start and end

Fixes #62211

Fixes #81911

Fixes #81949

Fixes https://github.com/microsoft/vscode/issues/73580