Retrieve the page favicons from the browser and display it on the tab selector

[canova]

This requires changes from Bug 1921778 since it adds the webchannel changes in the backend.

This PR adds the ability to retrieve the favicons for pages as a data url, so we can display them easily in the frontend without needing to fetch them from their url every time we open a profile.

This also changes how we use the Icon component and how we compute the css class names for them. Let me know what you think!

Note that this doesn't change the other icons that we have in places like call tree. I would prefer to do it as a followup as there are some questions to answer there.

Deploy preview with the page data retrieved already

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.09901% with 10 lines in your changes missing coverage. Please review.

Project coverage is 88.56%. Comparing base (84721b5) to head (a1488db). Report is 21 commits behind head on main.

Files with missing lines	Patch %	Lines
src/test/fixtures/mocks/web-channel.js	53.84%	6 Missing :warning:
src/utils/base64.js	80.00%	2 Missing :warning:
src/actions/icons.js	95.45%	1 Missing :warning:
src/reducers/profile-view.js	80.00%	1 Missing :warning:

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5166   +/-   ##
=======================================
  Coverage   88.56%   88.56%           
=======================================
  Files         307      308    +1     
  Lines       27936    28012   +76     
  Branches     7560     7578   +18     
=======================================
+ Hits        24742    24810   +68     
- Misses       2977     2985    +8     
  Partials      217      217           

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