[core] Wrap Instance in Arc and store it in Adapter

[sagudev]

Connections
Needed for #9950

Description
Currently global enforces drop order so that instance is dropped last:

wgpu/wgpu-core/src/global.rs

Line 39 in 4fe6176

// the instance must be dropped last

But when global is avoided we need to enforce this manually. We already need some of it's data in Adapter so this allows us to remove it. The new ownership chain that fixes the issue in #9950 is Queue -> Device -> Adapter -> Instance.

Testing
Should be covered by existing tests and new ownership chain fixes the problem in #9950.

Squash or Rebase?

Squash

Checklist

• I self-reviewed and fully understand this PR.
• WebGPU implementations built with wgpu may be affected behaviorally.
• Validation and feature gates are in place to confine behavioral changes.
• Tests demonstrate the validation and altered logic works.
• CHANGELOG.md entries for the user-facing effects of this change are present.
• The PR is minimal, and doesn't make sense to land as multiple PRs.
• Commits are logically scoped and individually reviewable.
• The PR description has enough context to understand the motivation and solution implemented.