fix(sql): fix queries where value legitimately begins with $

[fergusean]

Summary of changes

There are legitimate cases where a value may begin with $, and the current reference implementation breaks those cases. Example case, I have a query that looks for duplicate products named $100 Gift Card. This should result in:

WHERE `products`.`name` = ?

but it instead translates into:

WHERE `products`.`name` = `products`.`100 GC`

This PR introduces a new SqlReference class that can be used for cases where a reference is actually desired.

I only see a single usage case in the Deepkit source, and it's in the tests. It's unclear how many Deepkit users this may impact, but I do think it's important to fix.

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[marcj]

thanks @fergusean