Add max_color_attachments and max_color_attachment_bytes_per_sample

[nical]

Connections

• Spec discussion: maxColorAttachments not sufficient? gpuweb/gpuweb#2965
• Spec for color attachment bytes per sample: https://gpuweb.github.io/gpuweb/#abstract-opdef-calculating-color-attachment-bytes-per-sample

Description

This PR adds the two limits. max_color_attachment was already partially implemented via a constant in wgpu-hal. The render bundle code still uses that instead of the device limit so there is followup work to do.

For max_color_attachment_bytes_per_sample This does a best effort to pick reasonable defaults since the limit is largely undocumented for most platforms (See the linked gpuweb discussion). The general idea is that in doubt, 32 bytes is a safe assumption, and the limit is mostly to cater to tiled GPUs so on non-tiled ones we could increase the limits (for example d3d12 does not target non-tiled GPUs today).

Testing

The CTS covers these.

Checklist

• Run cargo fmt.
• Run cargo clippy.
• Run cargo xtask test to run tests.

[teoxoy]

LGTM