This separates the concern of two different "mode".
- UserIntent: focus on the overall goal of the build
- CompileMode: the actual compile operation for each unit
This is a preparation of adding `-Zno-link`/`-Zlink-only` support,
which we'll have `CompileMode::Link` but that doesn't make sense to
show up in `UserIntent`.
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 had a few locations where the shell was written to raw instead of
through the test harness or through other captured mechanisms. This
updates the test suite so testing Cargo with `--quiet` provides a nice
and clean report of tests executed.
