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.
---------
Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
# Objective
- Many of the items in the `ci` tool use `pub(crate)`, which is
functionally equivalent to `pub` when the crate is not a library.
- A few items are missing documentation.
## Solution
- Make all `pub(crate)` items just `pub`.
- `pub` is easier to type and less obscure, and there's not harm from
this change.
- Add / modify documentation on `CI`, `Prepare`, and `PreparedCommand`.
# Objective
- Currently all `ci` commands are in the `subcommands` module. This is
problematic when you want to implement actually subcommands (such as
`cargo r -p ci -- doc check`).
- All command modules include the `_command` suffix, which is redundant.
## Solution
- Move `commands` modules into root crate folder.
- Merge contents of `commands/mod.rs` into `main.rs`.
- Move `commands::subcommands` module into `commands` module.
- Remove the `_command` suffix from all `commands::subcommands` modules.
