Using Typescript & Centralizing Builds

[weaverryan]

Q	A
Bug fix?	No
New feature?	Yes
Tickets	None
License	MIT

Depends on #141

Hi!

This PR converts the project to use TypeScript, but that in itself wasn't really the motivation.

Motivations / Changes

• A) Standardize how we do things to be more like @hotwired/stimulus and other high-quality Stimulus libraries (like stimulus-use
• B) Centralize the build processes: the "build", "test" and "lint" processes are now all centralized so that each "library" can focus on just doing its job.
• C) This removes support for IE11 (see below).

B) Was the main motivator - before, each library was responsible for setting up their own test process and (more importantly) their own build process, which allowed for inconsistencies for what transformations we make, etc.

IE 11 Support Gone

Stimulus 3 dropped IE 11 support. This PR would be released with the version of Symfony UX that starts using Stimulus 3. So, we follow suit. It makes the builds smaller and makes (along with Typescript) our build process MUCH simpler.

It's pretty easy to see the difference in the built files - for example https://github.com/symfony/ux/pull/156/files#diff-72060cc03a17f489a2c7e84dd42fab25c7d19ee5154f0c493f00b91d6a13285b

TODOS

• Some additional cleanup so that the TypeScript build process finishes without warnings (it already finishes without errors).

[tgalopin]

Thanks @weaverryan.