Rename `pgx-utils` into something more meaningful, such as `pgx-sqlgen` or equivalent

[BradyBonnette]

Some work was done to remove a lot of dependencies out of the critical build path, as a result of https://github.com/tcdi/pgx/pull/645

Essentially pgx-utils was stripped of functionality that really could be implemented other spots. At the end of the day, pgx-utils now only contains code that handles internal SQL entities parsing/mappings.

Even though this would be a small refactor, it lends itself to something being named appropriately instead of generically.

[workingjubilee]

<joke>pgx-compiler</joke>

[Hoverbear]

@workingjubilee I think it could be billed as a transpiler. :smirk:

[workingjubilee]

@eeeebbbbrrrr weighed in and thinks that it might be preferable to keep pgx-utils for another round and try to whittle all of the crate down to nothing, moving components into pgx-macros, cargo-pgx, and pgx-pg-sys as appropriate.