Move Quest-specific types into the sequester projects

[Copilot]

Quest, Sequestered, and ContentScrubber types are action-specific and should not live in the shared DotNet.DocsTools project.

• Production code: Move these types into the sequester action project and use the Quest2GitHub namespaces.
• Tests: Move the corresponding Quest and ContentScrubber tests into the sequester test project.
• Shared support: Expose the response-extraction helpers needed by the relocated Quest models.

using Quest2GitHub.GitHubObjects;
using Quest2GitHub.Utility;

• Fixes Update actions to use commit SHAs #743

[Copilot]

Copilot wasn't able to review any files in this pull request. Check if the Files changed in this pull request are included in default exclusions.

[BillWagner]

This LGTM.

[BillWagner]

BTW, once we've finished these larger scale moves between repos, I am going to send Copilot on a task to write tests.