refactor: Add XRPL_RETIRE_FIX and XRPL_RETIRE_FEATURE

[a1q123456]

High Level Overview of Change

This PR makes it more clear by replacing XRPL_RETIRE with XRPL_RETIRE_FIX and XRPL_RETIRE_FEATURE.

Context of Change

Once we got confused because we didn't know whether we should prefix the feature amendments we retired with feature in XRPL_RETIRE() in features.macro, because we prefix retired fix amendments with fix.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Performance (increase or change in throughput and/or latency)
• Tests (you added tests for code that already exists, or your new feature included in this PR)
• Documentation update
• Chore (no impact to binary, e.g. .gitignore, formatting, dropping support for older tooling)
• Release

API Impact

• Public API: New feature (new methods and/or new fields)
• Public API: Breaking change (in general, breaking changes should only impact the next api_version)
• libxrpl change (any change that may affect libxrpl or dependents of libxrpl)
• Peer protocol change (must be backward compatible or bump the peer protocol version)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.6%. Comparing base (ff18cfe) to head (662b3aa).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop   #6014   +/-   ##
=======================================
  Coverage     78.6%   78.6%           
=======================================
  Files          817     817           
  Lines        68995   68995           
  Branches      8239    8239           
=======================================
  Hits         54221   54221           
  Misses       14774   14774           

Files with missing lines	Coverage Δ
include/xrpl/protocol/Feature.h	97.9% <ø> (ø)
src/libxrpl/protocol/Feature.cpp	94.6% <ø> (ø)

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[pratikmankawde]

LGTM