Replace hide/show password text with eye icons

[rebecca-shoptaw]

Closes #9533.

Feature. Switches out "Hide Password"/"Show Password" text for some simple eye open/closed icons.

Technical

• Went with Material Design icons to match the mockup
• Involved moving the password-visibility-toggle class from the a element to its img child so that the JavaScript would activate on the correct element
• Would also be happy to do away with the a element entirely and just put a cursor: pointer on the img -- held off for now in case the image nested in link is the preferred pattern for icons

Testing

1. Go to /account/create
2. Begin typing a password -- by default the password should be hidden and you should see a closed-eye icon
3. Click on the icon -- the password should appear and the icon should switch to an open eye

Screenshot

Stakeholders

@cdrini

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.

Project coverage is 16.29%. Comparing base (1cd8f21) to head (b5f4c1b).
Report is 40 commits behind head on master.

Files	Patch %	Lines
...nlibrary/plugins/openlibrary/js/password-toggle.js	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9534      +/-   ##
==========================================
+ Coverage   16.17%   16.29%   +0.12%     
==========================================
  Files          90       90              
  Lines        4736     4761      +25     
  Branches      824      826       +2     
==========================================
+ Hits          766      776      +10     
- Misses       3453     3463      +10     
- Partials      517      522       +5     

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[cdrini]

Looks great! One small accessibility fix.

[cdrini]

Looks great! 👁️