Support wasm32-u-u on web via patching Cargo.toml?

[dhardy]

As I outlined here, we could support wasm32-unknown-unknown on web via patching Cargo.toml:

We publish getrandom-js with feature all-targets:

• For wasm32-unknown-unknown, this will assume a web (JS) target.
• For other targets without feature all-targets, this will compile_error!.
• For other targets with feature all-targets, this will depend on and use getrandom.

Users may enable this platform for getrandom by patching Cargo.toml as follows:

[patch.crates-io.getrandom]
version = "0.3"
package = "getrandom-wasm-js"

I think this approach will work, but it's untested. It does not support selection via cfg (e.g. env var) however.

This does not prevent us also supporting wasm32-u-u on web with the current solution (specifying getrandom_backend='wasm_js').

[dhardy]

For clarification: crates like rand which cannot assume anything about their target environment would depend on getrandom; the above patch is to replace this dependency.

Crates which can assume JS (web) may use getrandom-js directly.