Add support to install 3rd-party packages

[deathaxe]

Relational

In case a syntax embeds a 3rd-party syntax it might be required to install it to succeed related syntax tests.

Request

Add a variable like packages to pass a list of repositories to clone packages from.

    steps:
      - uses: actions/checkout@v2
      - uses: SublimeText/syntax-test-action@v2
        with:
          build: ${{ matrix.build }}
          default_packages: ${{ matrix.default_packages }}
          packages:
            - https://github.com/danro/LESS-sublime
            - https://github.com/braver/SublimeSass
            - ...

[michaelblyons]

Might require giving the packages specific names, too, yes?

[FichteFoll]

It will require the repo and optionally a ref and the name to install at, but quite possible indeed.

(I wonder at what point I will change the wrapper script to use Python.)

[FichteFoll]

This is now live in 2.2 after some fixes (via trial and error and an added test case in this repo).