We now include the prelude in so many places, this simplifies how we can
present how `cargo-test-support` works.
Yes, this included some `use` clean ups but its already painful enough
walking through every test file, I didn't want to do it twice.
While this is noisy and hides other deprecations, I figured deprecations would
make it easier for people to discover what tasks remain and allow us to
divide and conquer this work rather than doing a heroic PR.
In theory, this will be short lived and we'll go back to seeing
deprecations in our tests.
We already refer to test targets as "test targets" instead of "tests" in
`--test` but not `--tests` or in the error output. This makes it
uniformly refer to them as "test targets", making it clearer that these
aren't test functions.
Fixes#7864
