fix: DDL comments to be recorded in AST

[harshit-gangal]

Description

There were few AST where comments parsed were not stored in the AST.
This PR fixes those statements
like create index, drop index and alter database.
Also modified the comment position for create database aligning with other syntax.

Related Issue(s)

• feat: authoritative query timeout for vttablet from vtgate #16735

Checklist

• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 68.92%. Comparing base (d9e59b6) to head (698a52a).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
go/vt/sqlparser/ast_format.go	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16774      +/-   ##
==========================================
- Coverage   68.94%   68.92%   -0.03%     
==========================================
  Files        1565     1565              
  Lines      201764   201764              
==========================================
- Hits       139112   139066      -46     
- Misses      62652    62698      +46     

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