corrosion_add_cxxbridge does not respect crate features

[FabianHummel]

corrosion_import_crate(
        MANIFEST_PATH example_path/Cargo.toml
        FEATURES interop) # Note this feature flag here
        
corrosion_add_cxxbridge(example-bridge
        CRATE example
        MANIFEST_PATH example_path
        FILES ffi.rs)

[package]
name = "example"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib", "lib"]

[features]
interop = ["dep:cxx", "dep:cxx-build"] # We lock cxx features behind this feature flag.

[dependencies]
cxx = { version = "1.0.135", optional = true }

[build-dependencies]
cxx-build = { version = "1.0.135", optional = true }

https://github.com/corrosion-rs/corrosion/blob/999f93b98e965dc418b43854ad321a4e45385983/cmake/Corrosion.cmake#L1674C1-L1680C6

The command that is run in the code linked above (/Users/.../.rustup/toolchains/nightly-aarch64-apple-darwin/bin/cargo tree -i cxx --depth=0) returns the error described below, because cxx is locked behind the interop feature flag.

error: package ID specification 'cxx' did not match any packages

	Did you mean 'syn'?

It can be fixed by adding the features that are passed to corrosion_import_crate to the cargo tree command, so it looks like this: /Users/.../.rustup/toolchains/nightly-aarch64-apple-darwin/bin/cargo tree -i cxx --features interop --depth=0 which then returns the correct cxx version: cxx v1.0.135

Why lock cxx behind a feature flag?

My crate is being cross-compiled to many different platforms and contains lots of shared code for either WebAssembly (wasm-bindgen) and C++ (cxx) which needs to be toggled based on where it's built.

[jschwe]

My crate is being cross-compiled to many different platforms and contains lots of shared code for either WebAssembly (wasm-bindgen) and C++ (cxx) which needs to be toggled based on where it's built.

The same use case could also be solved by dependencies conditional per target-triple, so I guess we should also respect the target / or pass --target all