Support /BrotliDecode filter

[guustysebie]

Implementation for /BrotliDecode filter

This patch allows to work with the brotli encoded streams, also no clue on how your test framework is supposed to work so I added a few test files but not sure. any guidance would be nice

[timvandermeij]

The procedure for adding reference tests, so basically screenshot tests, is:

1. Add the file(s) with Brotli encoding in test/pdfs.
2. Add the file(s) to test/pdfs/.gitignore.
3. Add the file(s) to test/test_manifest.json as eq-type tests, similar to existing entries.

[calixteman]

I didn't review the patch for now.
As a first feedback, we don't want to include some code we don't control.
So it's ok to use the code from the google repo, the MIT license is compatible with ours and we can trust the code, but we want to have a script in order to make a release ourselves.
We'd need to have a new task in the gulp file in order to fetch the code from the repo based on a gh hash.
We need to have license stuff, readme, ... similarly to what we've for openjpeg, jbig2, ...
I don't think we need a separate repo (like we've for openjpeg, ...) so just a small script should be fine.
And the last thing, we don't want to you the minified version.

If for whatever reason, you aren't able to do that, then tell us and we'll do that.
Thank you.