Fix setting instance validation flags (fixed #533)

[lisyarus]

Checklist

• cargo clippy reports no issues
• cargo doc reports no issues
• cargo deny issues have been fixed or added to deny.toml
• Human-readable change descriptions added to CHANGELOG.md under the "Unreleased" heading.
  • If the change does not affect the user (or is a process change), preface the change with "Internal:"
  • Add credit to yourself for each change: Added new functionality. @githubname

I couldn't find the CHANGELOG.md file. Should I create it?
Also, it seems that the correct command is not cargo deny, but cargo deny check.

Description

This changes how instance flags are mapped to wgt::InstanceFlags. The behavior of old flags doesn't change, but now

• An instance can actually be created with empty flags
• Some new flags supported by wgt::InstanceFlags were added that were previously missing
• Extra convenience bitfields were added that map to wgt::InstanceFlags::debugging()/advanced_debugging()/with_env()

Related issues

This fixes #533.

[cwfitzgerald]

Very nice!