fix: set role annotation and add inline unfold to nls

[akoreman]

Two small fixes:

• Adds 'button' role to gutter annotations.
• Adds title of inline unfold button to the externalized translations.

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[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (d455e9b) 86.98% compared to head (31a6d64) 86.98%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5176   +/-   ##
=======================================
  Coverage   86.98%   86.98%           
=======================================
  Files         565      565           
  Lines       45103    45107    +4     
  Branches     6931     6931           
=======================================
+ Hits        39231    39235    +4     
  Misses       5872     5872           

Flag	Coverage Δ
unittests	86.98% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/layer/gutter.js	90.69% <100.00%> (+0.08%)	⬆️
src/layer/text.js	91.78% <100.00%> (+0.01%)	⬆️

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