They've been deprecated for four years.
This commit includes the following changes.
- It eliminates the `rustc_plugin_impl` crate.
- It changes the language used for lints in
`compiler/rustc_driver_impl/src/lib.rs` and
`compiler/rustc_lint/src/context.rs`. External lints are now called
"loaded" lints, rather than "plugins" to avoid confusion with the old
plugins. This only has a tiny effect on the output of `-W help`.
- E0457 and E0498 are no longer used.
- E0463 is narrowed, now only relating to unfound crates, not plugins.
- The `plugin` feature was moved from "active" to "removed".
- It removes the entire plugins chapter from the unstable book.
- It removes quite a few tests, mostly all of those in
`tests/ui-fulldeps/plugin/`.
Closes#29597.
internal: port anymap
## Description
- The anymap crate has been ported. During this process, unnecessary features for rust-analyzer have been removed.
- From the tests that were checking the existing licenses, the anymap license (`BlueOak-1.0.0 OR MIT OR Apache-2.0`) has been removed.
## Requests
- While porting the code this time, I have tried to respect the original author's intentions and have kept the comments/codes as much as possible. Please don't hesitate to tell me if you think the comments/codes also need to be appropriately modified.
- If there are any necessary changes regarding the licensing or anything else, please let me know so I can fix them.
## Issue
https://github.com/rust-lang/rust-analyzer/issues/15500
Switch to in-tree rustc dependencies with a cfg flag
We can use this flag to detect and prevent breakages in rustc CI. (see #14846 and #15569)
~The `IN_RUSTC_REPOSITORY` is just a placeholder. Is there any existing cfg flag that rustc CI sets?~
