Update code and documentation to Sublime Text 4 and Xdebug 3

[gitressa]

Between version 2 and 3 of Xdebug, many things changed, so the code and documentation needs to get updated: https://xdebug.org/docs/upgrade_guide

The code should probably also get a check up, to make sure it works with Sublime Text 4.

Remaning tasks

• Update code to Xdebug 3
• Update code to work with Sublime Text 4
• Update the documentation

[maliayas]

FWIW I can use SublimeTextXdebug 1.1.2 (commit 6b7e8f4) with Xdebug 3.1.6 on PHP 7.4 just fine. I guess this means Xdebug protocol hasn't changed much from 2 to 3. I'm on ST3 btw.