Auto merge of #10776 - Muscraft:cache-workspace-discovery, r=weihanglo

Auto merge of #10776 - Muscraft:cache-workspace-discovery, r=weihanglo

add a cache for discovered workspace roots

## History
`@ehuss` [noticed that](https://github.com/rust-lang/cargo/pull/10736#discussion_r894071933) workspace inheritance caused a significant increase in startup times when using workspace inheritance. This brought up the creation of #10747.

When using a similar test setup [to the original](https://github.com/rust-lang/cargo/pull/10736#discussion_r894822022) I got
```
Benchmark 1: cd rust; ../../../target/release/cargo metadata
  Time (mean ± σ):     149.4 ms ±   3.8 ms    [User: 105.9 ms, System: 31.7 ms]
  Range (min … max):   144.2 ms … 162.2 ms    19 runs

Benchmark 2: cd rust-ws-inherit; ../../../target/release/cargo metadata
  Time (mean ± σ):     191.6 ms ±   1.4 ms    [User: 145.9 ms, System: 34.2 ms]
  Range (min … max):   188.8 ms … 193.9 ms    15 runs
```

This showed a large increase in time per cargo command when using workspace inheritance.

During the investigation of this issue, other [performance concerns were found and addressed](https://github.com/rust-lang/cargo/pull/10761). This resulted in a drop in time across the board but heavily favored workspace inheritance.
```
Benchmark 1: cd rust; ../../../target/release/cargo metadata
  Time (mean ± σ):     139.3 ms ±   1.7 ms    [User: 99.8 ms, System: 29.4 ms]
  Range (min … max):   137.1 ms … 144.5 ms    20 runs

Benchmark 2: cd rust-ws-inherit; ../../../target/release/cargo metadata
  Time (mean ± σ):     161.7 ms ±   1.4 ms    [User: 120.4 ms, System: 31.2 ms]
  Range (min … max):   158.0 ms … 164.6 ms    18 runs
```

## Performance after changes
`hyperfine --warmup 10 "cd rust; ../../../target/release/cargo metadata" "cd rust-ws-inherit; ../../../target/release/cargo metadata" --runs 40`
```
Benchmark 1: cd rust; ../../../target/release/cargo metadata
  Time (mean ± σ):     140.1 ms ±   1.5 ms    [User: 99.5 ms, System: 30.7 ms]
  Range (min … max):   137.4 ms … 144.0 ms    40 runs

Benchmark 2: cd rust-ws-inherit; ../../../target/release/cargo metadata
  Time (mean ± σ):     141.8 ms ±   1.6 ms    [User: 100.9 ms, System: 30.9 ms]
  Range (min … max):   138.4 ms … 145.4 ms    40 runs
```

[New Benchmark](https://github.com/rust-lang/cargo/pull/10754)
`cargo bench -- workspace_initialization/rust`
```
workspace_initialization/rust
    time:   [14.779 ms 14.880 ms 14.997 ms]
workspace_initialization/rust-ws-inherit
    time:   [16.235 ms 16.293 ms 16.359 ms]
```

## Changes Made
- [Pulled a commit](https://github.com/rust-lang/cargo/pull/10736/commits/bbd41a4dca8e001c8a45979c563293ef0a5c0d77) from `@ehuss` that deduplicated finding a workspace root to make the changes easier
- Added a cache in `Config` to hold found `WorkspaceRootConfig`s
  - This makes it so manifests should only be parsed once
- Made `WorkspaceRootConfig` get added to the cache when parsing a manifest

## Testing Steps
To check the new benchmark:
1. `cd benches/benchsuite`
2. `cargo bench -- workspace_initialization/rust`

Using `hyperfine`:
1. run `cargo build --release`
2. extract `rust` and `rust-ws-inherit` in `benches/workspaces`
3. cd `benches/workspaces`
4. Prime the target directory with a cache of `rustc` info. In `rust` and `rust-ws-inherit`, run: `cargo +nightly c -p linkchecker`. Otherwise it would be measuring `rustc` overhead.
4. run `hyperfine --warmup 10 "cd rust; ../../../target/release/cargo metadata" "cd rust-ws-inherit; ../../../target/release/cargo metadata" --runs 40`

closes #10747