Standardize NIST guidance sentence order in crypto XML docs

[Copilot]

This stacked PR addresses review feedback on #12524 by updating the exact NIST guidance sentence wherever it appears in the affected crypto docs. The goal is a wording-only normalization with no semantic changes.

• Scope of change

  • Updated all matching occurrences in xml/System.Security.Cryptography/* from:
    • See [NIST SP 800-131A Rev. 2](...) for guidance on approved algorithms.
  • To:
    • For guidance on approved algorithms, see [NIST SP 800-131A Rev. 2](...).

• What was touched

  • 18 XML doc files in System.Security.Cryptography.
  • Changes are limited to sentence ordering in existing warning/remarks text; links and surrounding guidance remain intact.

• Example update

  Due to collision problems with MD5, Microsoft recommends using a NIST-approved hash function.
  For guidance on approved algorithms, see [NIST SP 800-131A Rev. 2](https://csrc.nist.gov/pubs/sp/800/131/a/r2/final).

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-security, @vcsjones