Parse SRID attribute for virtual columns

[dbussink]

The parser is missing support to parse the SRID attribute for a virtual column. This adds the logic.

Related Issue(s)

Fixes #17678

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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• Tests were added or are not required
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• Documentation was added or is not required

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.75%. Comparing base (cb7d61a) to head (ae3d283).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17680      +/-   ##
==========================================
- Coverage   67.75%   67.75%   -0.01%     
==========================================
  Files        1587     1587              
  Lines      255780   255780              
==========================================
- Hits       173310   173291      -19     
- Misses      82470    82489      +19     

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