In Context::handle_error_fatal, print cause chain.

[kpreid]

Checklist

• Run cargo clippy.
• Run RUSTFLAGS=--cfg=web_sys_unstable_apis cargo clippy --target wasm32-unknown-unknown if applicable.
• Add change to CHANGELOG.md. See simple instructions inside file.

Connections
Fixes #3551.

Description
In Context::handle_error_fatal, print cause chain using the same formatting as for non-fatal errors.

Also add #[track_caller] so that the panic location is specific to the error.

Testing
Manually tested using an application with a deliberately introduced error. Example result:

thread 'main' panicked at 'Error in RenderBundleEncoder::finish: Validation Error

Caused by:
    In a set_pipeline command
      note: render pipeline = `BloomPipelines::downsample_pipeline`
    Render pipeline targets are incompatible with render pass
    Incompatible color attachment: the renderpass expected [] but was given [Some(Rgba16Float)]
', /Users/kpreid/Projects/rust/wgpu/wgpu/src/backend/direct.rs:2105:18
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Previously, the message would have ended at "In a set_pipeline command".

[kpreid]

One possible flaw in this PR is that some fatal errors probably should not be described as "Validation Error"s (which format_error currently does unconditionally). I don't know exactly which ones, though.

[cwfitzgerald]

Fatal errors are almost all not supposed to be fatal, we just haven't implemented non-fatality yet.