feat: add to_url_lossy to connect options

[lily-mosquitoes]

Add a get_url to ConnectOptions and implement it for all needed types; add get_filename for SqliteConnectOptions. These changes make it easier to test sqlx.

Does your PR solve an issue?

Fixes #2901
Related to #2764

[lily-mosquitoes]

This code uses unwrap on the Url::parse because it seems to me that the internal state of each of the types should always be valid. Let me know if that is not acceptable however, and I could change the response signature to a Result.

[abonander]

As mentioned in #2901, I'd like to see a motivating example to better understand the use-case for this, because not many tools use the same URL syntax that SQLx does.

[ahcodedthat]

See also #2097, another use case for this. Thanks for working on it!