Support for a new "close inactive tabs" command.

[mhammond]

The core foundation for CloseInactiveTabs - still to come:

• Teaching the tabs engine about the command
• Having Fenix support the command.

Pull Request checklist

• Breaking changes: This PR follows our breaking change policy
  • [ ] This PR follows the breaking change policy:
    • This PR has no breaking API changes, or
    • There are corresponding PRs for our consumer applications that resolve the breaking changes and have been approved
• [ ] Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• [ ] Tests: This PR includes thorough tests or an explanation of why it does not
• [ ] Changelog: This PR includes a changelog entry in CHANGELOG.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• [ ] Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due diligence applied in selecting them.

Branch builds: add [firefox-android: branch-name] to the PR title.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 93 lines in your changes missing coverage. Please review.

Project coverage is 22.58%. Comparing base (7e50de7) to head (c91c701).

Files	Patch %	Lines
...nts/fxa-client/src/internal/close_inactive_tabs.rs	0.00%	52 Missing :warning:
...lient/src/internal/commands/close_inactive_tabs.rs	0.00%	10 Missing :warning:
components/fxa-client/src/internal/device.rs	0.00%	10 Missing :warning:
components/fxa-client/src/internal/telemetry.rs	0.00%	10 Missing :warning:
components/tabs/src/storage.rs	0.00%	5 Missing :warning:
components/fxa-client/src/internal/commands/mod.rs	0.00%	4 Missing :warning:
components/fxa-client/src/push.rs	0.00%	2 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6281      +/-   ##
==========================================
- Coverage   22.65%   22.58%   -0.07%     
==========================================
  Files         331      333       +2     
  Lines       29794    29882      +88     
==========================================
  Hits         6750     6750              
- Misses      23044    23132      +88     

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[mhammond]

I think this is ready to roll!

[mhammond]

This is also in #6289, so let's kill this and land it all together.