Unify all Hyprland code w.r.t. code styling guidelines (c.f. #9522)

[ninetailedtori]

Describe your PR, what does it fix/add?

#9061 - Unification of code styling guidelines w.r.t. our contribution rulesets. This is a major refactoring change, and as such will likely be quite broken until everything is fixed. There were also a ton of typos and grammatical fixes I included.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

• There are a LOT of variable name changes, which are still happening in this PR. There WILL be breakages.
• clang-format and clang-tidy, I'd like to update them to a newer version in our GH workflows as well, but don't know too much about it. I threw a few errors with formatting on my own fork, regarding things like ReflowComments: 'Indent' etc.
• There are some additions of files. These are just forward declarations in header and creation of source files. This is to reduce compile times and stay consistent with style guidelines.

Is it ready for merging, or does it need work?

• Complete?
• Tested?
• Supported testing from others?
• Patches required?
• Patches done?
• Merged?