Converts the CLDR locale extraction script to a Bazel tool.
This allows us to generate locale files within Bazel, so that
locales don't need to live as sources within the repo. Also
it allows us to get rid of the legacy Gulp tooling.

The migration of the Gulp script to a Bazel tool involved the
following things:

  1. Basic conversion of the `extract.js` script to TypeScript.
     This mostly was about adding explicit types. e.g. adding `locale:
     string` or `localeData: CldrStatic`.

  2. Split-up into separate files. Instead of keeping the large
     `extract.js` file, the tool has been split into separate files.
     The logic remains the same, just that code is more readable and
     maintainable.

  3. Introduction of a new `index.ts` file that is the entry-point
     for the Bazel tool. Previously the Gulp tool just generated
     all locale files, the default locale and base currency files
     at once. The new entry-point a...