Detect sysroot dependencies using symlink copy
cc #7637
It is currently in a proof of concept stage, and it doesn't generates a copy. You need to provide your own sysroot copy in `/tmp/ra-sysroot-hack` in a way that `/tmp/ra-sysroot-hack/library/std/lib.rs` exists and `/tmp/ra-sysroot-hack/Cargo.toml` is [the one from this comment](https://github.com/rust-lang/rust-analyzer/issues/7637#issuecomment-1495008329). I will add the symlink code if we decide that this approach is not a dead end.
It seems to somehow work on my system. Go to definition into std dependencies works, type checking can look through fields if I make them public and `cfg_if` appears to work (I tested it by hovering both sides and seeing that the correct one is enabled). Though finding layout of `HashMap` didn't work.
Please try it and let me know if I should go forward in this direction or not.
fix: allow new, subsequent `rust-project.json`-based workspaces to get proc macro expansion
As detailed in https://github.com/rust-lang/rust-analyzer/issues/14417#issuecomment-1485336174, `rust-project.json` workspaces added after the initial `rust-project.json`-based workspace was already indexed by rust-analyzer would not receive procedural macro expansion despite `config.expand_proc_macros` returning true. To fix this issue:
1. I changed `reload.rs` to check which workspaces are newly added.
2. Spawned new procedural macro expansion servers based on the _new_ workspaces.
1. This is to prevent spawning duplicate procedural macro expansion servers for already existing workspaces. While the overall memory usage of duplicate procedural macro servers is minimal, this is more about the _principle_ of not leaking processes 😅.
3. Launched procedural macro expansion if any workspaces are `rust-project.json`-based _or_ `same_workspaces` is true. `same_workspaces` being true (and reachable) indicates that that build scripts have finished building (in Cargo-based projects), while the build scripts in `rust-project.json`-based projects have _already been built_ by the build system that produced the `rust-project.json`.
I couldn't really think of structuring this code in a better way without engaging with https://github.com/rust-lang/rust-analyzer/issues/7444.
