feat(api): promote `psql` to a public API

[cpcloud]

This PR promotes ibis.util.psql to a public ibis.psql API.

It also fixes the fact that we are writing out the generic sqlglot dialect instead of writing the output in the desired input dialect.

[kszucs]

I'm not sure that we should place SQL prettifier utilities under the core ibis.expr package. The internals should be about the ibis internal representation nothing else (like the scope and timecontext files should be moved to the pandas backend and the random.py should be in the api.py).

Could we place it under ibis.common perhaps?

[github-actions[bot]]

Test Results

       35 files         35 suites   1h 10m 2s :stopwatch:   8 916 tests   7 119 :heavy_check_mark: 1 797 :zzz: 0 :x: 32 646 runs  25 802 :heavy_check_mark: 6 844 :zzz: 0 :x:

Results for commit ea0dbf0b.

:recycle: This comment has been updated with latest results.

[cpcloud]

We can certainly move this under ibis.common

[kszucs]

@cpcloud needs a rebase