Improved translation text editor

### Describe the problem

The current editor lacks some of the features that would be nice to have like:

* https://github.com/WeblateOrg/weblate/issues/12568
* https://github.com/WeblateOrg/weblate/issues/7797

It also sometimes suffers with highlighting overlay getting out of sync with the content (haven't seen this for a while, but it was recurring issue for years).

### Solution brainstorm

Let's look into other options for editors. What would be the perfect solution?

* Syntax highlighting for several formats (XML, HTML, reStructuredText, Markdown, ...)
* Highlighting/freezing placeables from the source string (https://github.com/WeblateOrg/weblate/issues/7797)
* Replacing and inserting values from JavaScript (visual keyboard, automatic suggestions, check fixes, ...)
* Whitespace chars help (non-breakable or zero-width spaces, text direction changes, ...) (https://github.com/WeblateOrg/weblate/issues/12568)

Bonus points:

* The search input also needs changes, but I'm not convinced that there is something to share (see https://github.com/WeblateOrg/weblate/issues/3063).

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

_No response_