migrate wasm example to trunk

[spookyvision]

Description

This PR migrates the wasm example from an npm/webpack based approach to trunk. Fixes #834.

Of note:
the console_error_panic_hook dependency was gated in Cargo.toml via [target."cfg(debug_assertions)".dependencies]. This is documented as nonfunctional and will throw a warning on build:

warning: Found `debug_assertions` in `target.'cfg(...)'.dependencies`. 
This value is not supported for selecting dependencies and will not work as expected. 
To learn more visit https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#platform-specific-dependencies

Since the actual usage of console_error_panic_hook is also gated in lib.rs behind #[cfg(debug_assertions)] it didn't make sense to have the cargo gate in place, hence I have removed it.

Next steps

If this PR is merged, the wiki page linked in the root README should be updated as well.

[est31]

Thanks for your PR. There is a bunch of build failures in CI, especially around wasm, could you have a look?

[spookyvision]

Thanks for your PR. There is a bunch of build failures in CI, especially around wasm, could you have a look?

I'm only seeing asmjs-wasm32-test fail and there's this message in the log:

error: component 'rust-std' for target 'asmjs-unknown-emscripten' is unavailable for download for channel 'stable'

this seems entirely unrelated to my PR…

as a side note though, trunk uses wasm-bindgen, which in turn only works with thewasm32-unknown-unknown target, so asmjs-unknown-emscripten is unsupported.

[est31]

Hmmm yeah fair points. Let's merge this.