Remove exposed C symbols from renderpass/computepass recording

[Wumpf]

Connections

• Most of Using multiple major versions of wgpu causes linker errors #3105

Description
There was a seemingly random assortment of C symbols exported from wgpu around command encoding. The C methods were already hardly usable since they first require initialization of objects that can only be created from Rust.
I noticed this a few weeks prior as unintentionally exported symbols on applications and libraries that use wgpu and the issue described in #3105 is caused by this.
The wgpu crate's wgpu-core implementation as well as wgpu-native rely on these methods, but not the fact that they're exported and #[no_mangle].

Removing the FFI opens a few small clean-up opportunities and less unsafe code here.

EDIT: This PR leaves intentionally leaves out bundles because firefox still relies on this. See comment below

Testing
It compiles!

The real test here is the review - am I missing something and these need to stick around?

Checklist

• Run cargo fmt.
• Run cargo clippy. If applicable, add:
  • --target wasm32-unknown-unknown
  • --target wasm32-unknown-emscripten
• Run cargo xtask test to run tests.
• Add change to CHANGELOG.md. See simple instructions inside file.

[cwfitzgerald]

I think Firefox relies on this, so we can't back this out without confirming with them.

[Wumpf]

Pulled firefox source now to have a look at: Firefox has its own ffi layer https://hg.mozilla.org/mozilla-central/file/tip/gfx/wgpu_bindings/src/command.rs which again falls the methods from compute_ffi/render_ffi but does not rely on them being exported on their own.

But best for some Mozilla folk to chime in and confirm. @jimblandy maybe since you commented on that ticket before?

[jimblandy]

@Wumpf Thanks for the ping. Since @nical changed command recording to never use wgpu in the content process, I think we may not need these any more, but let me check.

[jimblandy]

The #[no_mangle] declarations in wgpu-core/src/command/render.rs and compute.rs are no longer in use, and can be removed.

However, it seems like Firefox is still using wgpu-core/src/command/bundle.rs's #[no_mangle] functions from C++ code like this. It should be straightforward to fix these in the same way the render and compute recording function uses were removed.

[jimblandy]

I assume resolving this issue requires all #[no_mangle] attributes to be removed from wgpu-core. I've filed Bug 1887574 for getting that done.

[Wumpf]

thank you! I have some ongoing work that requires changes to the compute functions specifically in compute & render (follow-up to #5432 ) so I'll change this PR to clean up only those and we can take bundles at a later point in time.

[Wumpf]

all done and cleaned-up. Removed all FFI code now from compute & render, but didn't touch the bundle interface.
Removing ffi scaffolding resulted in quite a bit of streamlining!

[cwfitzgerald]

Amazing!

[cwfitzgerald]

Blocked on #5549