rust-analyzer doesn’t enable/pass a feature with `cargo.features` to a build script

Converting to an issue since I see no way this would be intended behavior, and I haven't been able to solve it myself.

I have "rust-analyzer.cargo.features": ["scrap/linux-pkg-config"] in a .vscode/settings.json, but it seemingly doesn't want to work.

Build script fails on this function, with VCPKG_ROOT not found..., which is code it shouldn't be getting to given that using pkg-config is enabled and I'm not setting NO_PKG_CONFIG_* anywhere.

Manually running the command does work:

» cargo check --workspace --message-format=json-diagnostic-rendered-ansi --manifest-path /path/to/Cargo.toml --keep-going --all-targets --features scrap/linux-pkg-config
(whole load of diagnostics text)

Using some logging suggests that the feature isn't being enabled at all after a server restart:

Caused by:
  process didn't exit successfully:...
  --- stdout
  Starting build script...
...
  Checking config for linux-pkg-config feature: false
  Checking NO_PKG_CONFIG variable value: Err(NotPresent)
  Using homebrew
  target_os: linux, target_arch: x86_64

Originally posted by @4JX in https://github.com/rust-lang/rust-analyzer/discussions/18416

Reproduce the issue with the .vscode/settings.json cargo.features setting and the supplied cargo check command, then compare the rust-analyzer build invocation with the manual command. Use the referenced libs/scrap/build.rs logging to verify whether the feature reaches the build script; done means rust-analyzer passes scrap/linux-pkg-config and the build script observes it as enabled.