Improve <thread> functions reference

[Rageking8]

• Add leading sentence and backticks
• Simplify and improve links
• Add basic example for get_id
• Update syntax (see microsoft/STL/stl/inc/thread L200-L225):
  • Add missing this_thread:: for those in the std::this_thread namespace
  • Remove inline in sleep_for, and format it
  • Remove void sleep_until(const xtime *Abs_time); since it no longer exists
• Update metadata

[prmerger-automator]

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[learn-build-service-prod]

Learn Build status updates of commit d813e39:

✅ Validation status: passed

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docs/standard-library/thread-functions.md	✅Succeeded

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[prmerger-automator]

PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.

[v-regandowner]

@TylerMSFT - Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team