Ed25519ph and Ed25519ctx Support

[skmcgrail]

Description of changes:

• Add support for Ed25519ph and Ed25519ph where the digest is pre-computed and provided externally.
• Add support for Ed25519ctx from RFC 8032.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license and the ISC license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.58974% with 10 lines in your changes missing coverage. Please review.

Project coverage is 78.93%. Comparing base (94daeb2) to head (dce8cd8).

Files with missing lines	Patch %	Lines
crypto/fipsmodule/curve25519/curve25519.c	91.58%	9 Missing ⚠️
crypto/fipsmodule/curve25519/ed25519_test.cc	97.22%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #2120    +/-   ##
========================================
  Coverage   78.92%   78.93%            
========================================
  Files         610      610            
  Lines      105137   105270   +133     
  Branches    14911    14923    +12     
========================================
+ Hits        82983    83094   +111     
- Misses      21503    21522    +19     
- Partials      651      654     +3     

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[andrewhop]

General notes:

1. Missing service indicator tests for approved ph and unapproved ctx
2. Missing ACVP demo vectors
3. Double checking: can these new singing modes rely on the existing boringssl_ensure_eddsa_self_test or do we need a new ctx/ph specific self test?

[skmcgrail]

Addressed all outstanding comments and remaining work items.