395: First Phase of Tracing Transition r=kvark a=cwfitzgerald
## Connections
This is the wgpu-rs component of https://github.com/gfx-rs/wgpu/pull/740.
## Notable Changes
- Added annotations for non-trivial wrapper functions
- Enabled building all features on docs.rs
- Took a dep on tracing.
- Fixes an assert that randomly stopped compiling.
- Added env variable WGPU_CHROME_TRACING which will be a path to the output chrome trace, if the feature is enabled.
- Added feature which corresponds directly to wgc feature.
Co-authored-by: Connor Fitzgerald <connorwadefitzgerald@gmail.com>