Optimize binary with wasm-opt in release mode

[TimJentzsch]

Objective

Closes #196, unblocks TheBevyFlock/bevy_new_2d#312.

With wasm-opt, we can further increase the performance and reduce the file size of the Wasm binary we use for web builds.
This speeds ups the app both in-game and the loading times.

Solution

As a simple first solution, we add a hard-coded size optimization pass in release mode.
In future PRs, we can make this more configurable.

To the user, we log the time the optimization took as well as the file size reduction as percentage.

This is behind the wasm-opt feature flag (currently disabled by default), to give the user a way to turn this off and because this increases compile times of the CLI quite a bit.

[TimJentzsch]

On my laptop on a simple game example, it currently takes 250s and reduces the file size by 34%.

These numbers will probably change quite a bit with #199 though, so I wouldn't read into it too much at this stage.

[DaAlbrecht]

Same here

[BD103]

How do I use this? I ran cargo build -F wasm-opt then bevy build web --release, but it gave an error:

$ bevy build web --release
error: unexpected argument '--release' found

Usage: bevy build web

For more information, try '--help'.

[DaAlbrecht]

How do I use this? I ran cargo build -F wasm-opt then bevy build web --release, but it gave an error:

$ bevy build web --release

error: unexpected argument '--release' found



Usage: bevy build web



For more information, try '--help'.

Cant test it right now but if i remember correctly it was 'bevy build -r web'

[TimJentzsch]

How do I use this? I ran cargo build -F wasm-opt then bevy build web --release, but it gave an error:

$ bevy build web --release

error: unexpected argument '--release' found



Usage: bevy build web



For more information, try '--help'.

Cant test it right now but if i remember correctly it was 'bevy build -r web'

That's right, the --release flag needs to come before the web subcommand (because it can also be used on native builds)

[BD103]

Ah yup, bevy build --release web did the trick! This looks good, merge it once you're happy with the state it's in. :)