* wpgu: Initial implementation of PixelBender shader execution
The implementation is split across four crates:
* `ruffle_render` now holds the main PixelBender bytecode parsing
implementation (previously, this was in `ruffle_core`).
* `ruffle_core` holds some helper functions for converting between
AVM2 `Value`s and the PixelBender vector types.
* `naga-pixelbender` (newly created) constructs a Naga `Module`
from parsed PixelBender bytecode
* `ruffle_render_wgpu` sets up the render pipeline for the shader
constructed by `naga-pixelbender`, and actually executes the shader.
The Actionscript-side shader parameters are passed in through uniforms.
This allows us to cache the compiled `naga::Module` and associated
wgpu types inside `ShaderData`, when it's first created. Each invocation
of a `ShaderJob` only needs to create a bind group and render pass.
Limitations:
* Only a few of the PixelBender opcodes are implemented - however, this is
enough to get Stemlands cannon rotation working, as well as a cool
"donut" shader that I found and included as a test.
* PixelBender matrix types are not supported.
* Only BitmapData is supported as an input/output type - Flash Player
also supports using Vector and ByteArray
* ShaderJob execution is always synchronous.
* Adjust comments
* Address review comments
Aaron Hill