Misuse of Metal API in rendering preperation

[Kees-van-Beilen]

Summary

On MacOS (and iOS) roughly every frame the render pipeline allocates a new temporary buffer, it also reinterprets the currently used texture buffers. This is bad practise as when using the Metal framework MTLBuffers should persist as long as possible and not just a single frame. Also whilst the texture reinterpretations aren't costly at all they do make a small obj-c allocation every frame for every texture.

This might (but probably not directly) be related to the high cpu usage found in #10261

Additionally:

• An Apple Instruments metal allocations trace of the 3d_scene example can be found https://bevy.inpolen.nl/traces/3d_scene.trace.zip
• Debugging this yourself requires you to properly sign the executable

Bevy version

Tested on:

• 0d23d71 bevy 0.11.3
• 6178ce9
• cb64a4a bevy 0.17-dev (current main)
  All of these have the same bug

[Kees-van-Beilen]

I've confirmed that all metal api misuse is done by bevy. We should exam all code that creates /manages wgpu buffers (because one of these buffers is creating a StagingBuffer and doing that every frame) and code that creates new imageviews.