Update npm scripts.

[legodude17]

This adds a build:all-contrib script to auto build all contrib. It also changes build-core to build:core. Now the build script will run build:all-contrib and build:core. It also adds install-all to install in main and contrib.This makes the testing much easier and more straightforward.

[getify]

I don't prefer those names/assumptions because it only works this way if you retrieve the whole repo via git.

If instead someone does an npm-install of just the core repo, they don't get contrib. so in that npm directory when they try to run tests, there won't be any contrib at all, so it's gonna fail.

I understand the concern of being confused that, when cloning from git, you have to go in and separately run the build of contribs. But I'm not sure this direction is the right way to go, because it will create failures/confusion in other use-case paths like npm-only consumption.

I'm happy to explore if there's some way to address both by somehow making it smart of enough to figure out which case we're in, but as this PR stands, it doesn't fit the bill.

[legodude17]

Do you think that something should be done? There could be a file that would do that that wouldn't be included in the npm package. Closing for now.