Text Fragments from highlight experimental feature

[schu96]

Closes #1363

Should allow users to highlight within the bookreader's text and generate a link with URI encoded parameters. The link is automatically copied to the user's clipboard and available for sharing with fellow patrons or new readers.

A test suite that validates the text fragment generation work is partially completed, just need some more specific example data to cover the remaining cases

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 79 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.19%. Comparing base (5c571e0) to head (203b2de).

Files with missing lines	Patch %	Lines
src/util/TextSelectionManager.js	55.83%	53 Missing ⚠️
src/plugins/url/UrlPlugin.js	27.27%	16 Missing ⚠️
src/plugins/url/plugin.url.js	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1504      +/-   ##
==========================================
- Coverage   69.70%   69.19%   -0.51%     
==========================================
  Files          65       65              
  Lines        5373     5512     +139     
  Branches     1182     1209      +27     
==========================================
+ Hits         3745     3814      +69     
- Misses       1594     1664      +70     
  Partials       34       34              

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[cdrini]

1. We should put this behind a plugin.experiment for "show highlight menu" ; see https://github.com/internetarchive/bookreader/pull/1481/files for example of how we might do this
2. We'll need this to work with the urlMode = history that prod uses; I'll set up a testbed for that.
3. Use a different icon / designs