This is a follow up fix for #17330 and fixes#17780.
There was a logic error in the ambiguity detection of
`cargo-manifest-proc-macros`.
`cargo-manifest-proc-macros` now has a test for this case to prevent the
issue in the future.
I also opted to hard fail if the `cargo-manifest-proc-macros` crate
fails. That way the error is more obvious and easier to fix and
diagnose.
## Testing
- The reproducer:
https://github.com/bevyengine/bevy_editor_prototypes/pull/178 works for
me using these fixes.
This pr uses the `extern crate self as` trick to make proc macros behave
the same way inside and outside bevy.
# Objective
- Removes noise introduced by `crate as` in the whole bevy repo.
- Fixes#17004.
- Hardens proc macro path resolution.
## TODO
- [x] `BevyManifest` needs cleanup.
- [x] Cleanup remaining `crate as`.
- [x] Add proper integration tests to the ci.
## Notes
- `cargo-manifest-proc-macros` is written by me and based/inspired by
the old `BevyManifest` implementation and
[`bkchr/proc-macro-crate`](https://github.com/bkchr/proc-macro-crate).
- What do you think about the new integration test machinery I added to
the `ci`?
More and better integration tests can be added at a later stage.
The goal of these integration tests is to simulate an actual separate
crate that uses bevy. Ideally they would lightly touch all bevy crates.
## Testing
- Needs RA test
- Needs testing from other users
- Others need to run at least `cargo run -p ci integration-test` and
verify that they work.
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Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
