Improvements for Console Variables

[AvarianKnight]

Goal of this PR

This PR has multiple different objectives.

1. Unify the Console Variable getters to one common file, fixing the main blocker for GET_CONVAR_FLOAT as was listed in #1255
2. Add GET_CONVAR_FLOAT so we can get console variables as floats.
3. Add a way to listen to Console Variable changes so we don't have to poll for them.

How is this PR achieving the goal

Does everything listen above.

This PR applies to the following area(s)

Server, FiveM, RedM

Successfully tested on

Game builds: N/A

Platforms: Windows

Checklist

• [x] Code compiles and has been tested successfully.
• [x] Code explains itself well and/or is documented.
• [x] My commit message explains what the changes do and what they are for.
• [x] No extra compilation warnings are added by these changes.

[martonp96]

Tested, working. Thank you for the contribution.