✨ Draw Invisibles Only On Selection

### Description

Some editors allow users to only see invisible characters in their selected text. Right now, CETV can only enable them for the entire document, or not at all.

### Alternatives Considered

_No response_

### Additional Context

Some updated requirements:
- The line fragment renderer will need to know about selected ranges, this introduces an interesting dependency tree.
- Querying selected ranges may be slow when it's done for *every* visible line fragment each render loop. The implementation should consider this or profile it to make sure it's negligible.

### Screenshots

_No response_