feat: Implement MariaDB ALTER TABLE syntax

[LeoniePhiline]

Implement MariaDB & MySQL ALTER TABLE syntax

Replacing the accidentally merged #98.

This PR is a draft just to show I'm working on that, since now other PRs have been merged and no parser code clashes await.

Fixes:

• Keyword CHANGE is missing (ALTER TABLE) #82
• Keywords AFTER is missing; FIRST and AFTER not yet part of ALTER TABLE #83
• Missing syntax: ALTER TABLE ... MODIFY [ COLUMN ] ... #89
• Some more MariaDB syntax missing or inconsistent highlight #71

PR contents:

• fix: Lift ALTER TABLE combination restriction (only Postgres)
  Resolves comment: Keyword CHANGE is missing (ALTER TABLE) #82 (comment)
• feat: Add MariaDB/MySQL ALTER TABLE ... CHANGE ...
  Fixes: Keyword CHANGE is missing (ALTER TABLE) #82
• feat: Add MariaDB/MySQL ALTER TABLE ... MODIFY ...
  Fixes: Missing syntax: ALTER TABLE ... MODIFY [ COLUMN ] ... #89
• feat: Add MariaDB/MySQL ADD|CHANGE|MODIFY ... FIRST|AFTER ...
  Fixes: Keywords AFTER is missing; FIRST and AFTER not yet part of ALTER TABLE #83

[LeoniePhiline]

@DerekStride PTAL

[DerekStride]

One question otherwise LGTM