Improve CMFCButton class reference

[Rageking8]

Summary:

• Make all code blocks cpp for proper syntax highlighting
• Add backticks for certain terms and other minor fixes (stray characters, missing parenthesis, or extra spacing)
• Fix malformed headings and add missing backticks (for uniformity)
• Replace br elements with backslash
• Remove empty Remarks sections

[prmerger-automator]

@Rageking8 : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[prmerger-automator]

@Rageking8 : Thanks for your contribution! The author(s) and reviewer(s) have been notified to review your proposed change.

[learn-build-service-prod]

Learn Build status updates of commit bf45ae8:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/mfc/reference/cmfcbutton-class.md	✅Succeeded

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[ttorble]

@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

[TylerMSFT]

Thank you

[TylerMSFT]

#sign-off

Thank you @Rageking8. This area of the docs is lower priority. If you care to, I think the C++ STL library docs need attention.