Add brotlicffi support

[Laerte]

Fix #6263

[codecov]

Codecov Report

Merging #6269 (99f7165) into master (bf14935) will decrease coverage by 0.03%.
Report is 1 commits behind head on master.
The diff coverage is 50.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6269      +/-   ##
==========================================
- Coverage   88.91%   88.88%   -0.03%     
==========================================
  Files         161      161              
  Lines       11796    11802       +6     
  Branches     1914     1914              
==========================================
+ Hits        10488    10490       +2     
- Misses        964      968       +4     
  Partials      344      344              

Files	Coverage Δ
scrapy/downloadermiddlewares/httpcompression.py	89.56% <50.00%> (-1.51%)	⬇️
scrapy/utils/_compression.py	89.61% <50.00%> (-2.29%)	⬇️

[wRAR]

I guess we need an extra-deps job for PyPy?

[wRAR]

Or no, we install brotli* for regular tests.

[Laerte]

Or no, we install brotli* for regular tests.

Yeah I replaced the PyPy pinned version for this one, should I create extra-deps?

[Gallaecio]

Oh, so brotli and zstandard are here. It would be great if we could remove them from here and put them in the extra environments of tox.ini instead, to make sure Scrapy works without them. (this also applies to other packages here, but they are out of scope; in fact, zstandard is kind of out-of-scope, you could leave it here as well).