Fixes to "Using 3D transforms" page

[RespiteFromReality]

PR addresses #9159 and additional problems I found in the page.

Page: https://docs.godotengine.org/en/stable/tutorials/3d/using_transforms.html

First PR, so apologies for any mistakes or lack of contributing requirements.

Could really use a sanity check on the page examples, because the more I re-read the page, the more I felt like I was missing something, but when testing in engine, the existing examples do not work correctly.

Changes

1. Applied neonmoe's (see issue) updated camera image commit as a patch from their fork, as they never created a PR. (I can remove it or replace it with my own if preferred.)
2. Bullet example
   • Using linear_velocity from Rigidbody3D in both GDScript and C#.
   • Fixing variable capitalization in C#.
   • Added comments for Node type used.
3. Jump example
   • Fixing variable capitalization in C#.
   • Added comments for Node type used.
4. Text changes
   • Removed confusing forward direction comment.
   • Making axis reminders consistent between examples.
5. Strafe Left example
   • Using velocity from CharacterBody3D in both GDScript and C# instead of translate_object_local. The current example doesn't strafe left properly, but I don't really know why.
   • Added move_and_slide() to stay consistent with CharacterBody3D use.
   • Added comments for Node type used.
6. FPS Camera example
   • The rotation in this example is inverted on both axis, so decided to subtract it to make it work how FPS camera rotation should work.

[Calinou]

Looks good to me.

I'd appreciate a cursory review from @aaronfranke to make sure the coordinate space fixes are correct.

[aaronfranke]

Please read this to understand the conventions and why some things may be confused between them: https://docs.godotengine.org/en/stable/tutorials/assets_pipeline/importing_3d_scenes/model_export_considerations.html#d-asset-direction-conventions

For user code in Godot, we need to be consistent, preferably with the camera and global forward, and so this PR is correct.

[mhilbrunner]

Thanks for contributing, and thank you everyone for the reviews! Merged.