MySQL dialect: Add support for hash comments

[hansott]

See https://dev.mysql.com/doc/refman/8.4/en/comments.html

[iffyio]

LGTM! cc @alamb

[coveralls]

Pull Request Test Coverage Report for Build 11271561060

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.001%) to 89.316%

---

Totals
Change from base Build 11263581007:	0.001%
Covered Lines:	30145
Relevant Lines:	33751

---

💛 - Coveralls

[alamb]

Thank you @hansott and @iffyio