Include translations for JavaScript files in language packs

[ocean90]

This is supposed to fix #62.

As a first step parts of https://meta.trac.wordpress.org/changeset/7833/ are added to the ZipProvider class.

[codecov-io]

Codecov Report

Merging #108 into master will increase coverage by 1.38%.
The diff coverage is 98.71%.

@@             Coverage Diff              @@
##             master     #108      +/-   ##
============================================
+ Coverage     78.05%   79.43%   +1.38%     
- Complexity      333      354      +21     
============================================
  Files            23       24       +1     
  Lines           802      856      +54     
============================================
+ Hits            626      680      +54     
  Misses          176      176

Impacted Files	Coverage Δ	Complexity Δ
inc/ZipProvider.php	100% <100%> (+1.11%)	23 <0> (-4)	⬇️
inc/Export.php	98.61% <98.61%> (ø)	25 <25> (?)

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[swissspidy]

@ocean90 What do you think of the current approach so far?

[swissspidy]

@ocean90 Somehow I can't select you as a reviewer 🤔 Let me know what you think of the current PR.