Relabel build scripts and add a 'clean' script

[harmony7]

This PR attempts to clean up the build scripts a bit. These changes hope to help people who develop with it.

1. build → build:release - this builds the 'release' version of the runtime (fastly.wasm)

This has been positioned as a sibling to the build:debug, build:debug:info, and build:weval scripts.

The references to the build that existed in the following files have been updated:

.github/workflows/main.yml
.github/workflows/release-please.yml
tests/wpt-harness/run-wpt.sh

2. I've added a clean script that cleans out the build artifacts:

starling.wasm
fastly.wasm
fastly.debug.wasm
fastly-weval.wasm
fastly-ics.wevalcache
fastly-js-compute-*.tgz

3. I've added a new build script that calls the clean script followed by build:release, build:debug, and build:weval, and I've updated the directions in DEVELOPMENT.md to call this one script.