Add comments to query language

[TheMikeste1]

This PR adds comments to DQL. Comments start with // and can be on their own line or after another statement.

Resolves #1624
[1] and [2] are implemented. [3] can be performed by creating multiple single-line comments.

Example:

// This is a comment at the beginning
TABLE (time-played + 100) as long, rating as rate, length
// This is a comment
// This is a second comment
FROM #games or #gaming  // This is an inline comment
// This is a third comment
WHERE long > 150 and rate - 10 < 40
// This is a fourth comment

   // This is a comment with whitespace prior
SORT length + 8 + 4 DESCENDING, long ASC
// This is a comment at the end

[Li-Mingshuang]

It hasn't been added to the released version?

[holroy]

It hasn't been added to the released version?

The 0.5.64 release was from Nov 2023, and this was added to the master branch in Dec 2023, so no it hasn't been released yet.

I'm playing with some other pull requests, so I'm hoping there'll be a release in a week or so (if someone capable of doing that approves of those PR's to come and those already accepted). One vital change though which needs to be done before a new release is released is this fix of the repetition of inline fields which was introduced around 0.5.59, see #2216