Task: Add reporting the size of build changes on PRs

[joshgoebel]

Is your request related to a specific problem you're having?

Prism does this and it's super cool. We should start reporting the size of the compressed web build changes with PRs. Just to start to get a feel for when we increase and shrink the final build size.

The solution you'd prefer / feature you'd like to see added...

https://github.com/preactjs/compressed-size-action

Just the first one I found. GitHub actions sounds about right.

Any alternative solutions you considered...

None.

Additional context...

None.