Allow `bevy build web` to bundle multiple binary targets

[TimJentzsch]

cargo build can build multiple packages at once.

bevy build web only partially supports this: As it wraps cargo build, all the Wasm binaries will be built as intended, but the bindgen creation and folder bundling currently uses the bevy run web logic and only selects a single target.

Instead, we should create the bindings and bundle the folders for all binaries compiled by cargo build.

Note that we should only do this for binary targets (and examples), not libraries, benchmarks and tests.