Purity inference

[bhansconnect]

Still has a few warnings, but this gets the platform working with purity inference and huge code size gains.

[lukewilliamboswell]

Bug from CI

$ roc build ./examples/sound.roc --target=wasm32 --no-link
thread 'main' panicked at crates/compiler/mono/src/reset_reuse.rs:1269:42:
Expected symbol to have a layout. It should have been inserted in the environment already.
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace