Add jsonp support to textsel fetches

[cdrini]

CORS endpoint isn't enabled for protected endpoints, so need JSONP :/

[codecov[bot]]

Codecov Report

Merging #790 (32d1531) into master (367248e) will decrease coverage by 0.03%. The diff coverage is 0.00%.

:exclamation: Current head 32d1531 differs from pull request most recent head 0dfd0f6. Consider uploading reports for the commit 0dfd0f6 to get more accurate results

@@            Coverage Diff             @@
##           master     #790      +/-   ##
==========================================
- Coverage   70.12%   70.09%   -0.03%     
==========================================
  Files          59       59              
  Lines        5325     5327       +2     
  Branches     1039     1041       +2     
==========================================
  Hits         3734     3734              
- Misses       1573     1574       +1     
- Partials       18       19       +1     

Impacted Files	Coverage Δ
src/plugins/plugin.text_selection.js	69.65% <0.00%> (-0.98%)	:arrow_down:

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