Support is_true / is_false methods for boolean expressions

[belovaf]

Even crates.io has a lot of booleanProp.eq(true) expressions, for example:
github_secret_scanning.rs#L62
This leads to an additional bind parameter and slows down a query.
It would be very convenient (and better performance) to have functions is_true / is_false to be rendered as = true / = false.

[weiznich]

I would like to see hard numbers for the claim that additional bind parameters slow down the query. Otherwise this does not seem to be justified in any way, given that it would require us to start dealing to convert rust values to SQL string representations with is something that we really want to avoid.