Update 2D particles page for Godot 4.4

[skyace65]

This PR is an update, though mostly re-organizing of the 2D particle page for Godot 4.4. New images have all been taken in Godot 4.4, but a lot of this reorganization is relevant to 4.0 and onward, looks like this page wasn't gone through yet. Did the following:

• All out of date screenshots have been updated for Godot 4.4, all images have gone through squoosh compression
• Updated the text to reflect that CPUParticles2D is not going to be kept up to date going forward.
• Changed conversion instructions to be for going from CPU to GPU instead of vice versa, which while still doable isn't advised
• All settings related to ProcessMaterial have been split off into their own page given just how many settings there are for it
• There are notes on the ProcessMaterial 2D page and 3D page pointing to the other one
• The first section of the new page was taken straight out of the 3D process material page
• All ProcessMaterial settings have been reorganized into the current Godot 4.4 subsections and sub-subsections
• The description for Spin Velocity has been removed as it's no longer an option
• The only description that has been updated is angular velocity, which borrows some language from spin velocity. As far as I can tell they're the same setting just renamed, and spin was never taken out of this page when it should have been
• The Gif that was being used for Spin Velocity is now being used for angular velocity. It doesn't match 100% though, it looks like the particles are being spread a bit compared to only changing the angular velocity setting. I didn't want to take time to make a new gif but if people want I can just remove this one if it's considered too inaccurate

Other than what I did for Angular velocity no new settings descriptions have been made, and both pages are missing a lot and need to be updated further. For the sake of making a review easier and my lack of familiarity with the specifics of particles I figured a good first step would just be to get this all properly organized and make sure there's at least nothing inaccurate in the information that is given, rather than try to do everything at once.

[tetrapod00]

Images look good, as long as we don't care about the quick open icon being present.

I commented on obvious grammar, spelling, and inaccuracies I found.

There are a lot of style changes I'd like to make to match the new standard guidelines but I think that's fine to defer to keep the diff in this PR more straightforward.

[skyace65]

Applied most of tetrapods suggestions (commented on the one I didn't do) and the images showing the folder icon have been redone

[mhilbrunner]

"This PR is an update" :D Well, this is a merge!

As always, thank you (and thanks tetra for the reviews!)