Use project version inferred from POT import for translation API

[swissspidy]

Description

Extracts and stores the version number from the Project-Id-Version header if it exists in a POT file.

The version number is then used in the translation API responses.

How has this been tested?

Added unit tests to document the behavior.

Types of changes
New feature (non-breaking change which adds functionality)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code has proper inline documentation.

[codecov-io]

Codecov Report

Merging #133 into master will increase coverage by 0.28%.
The diff coverage is 94.11%.

@@             Coverage Diff              @@
##             master     #133      +/-   ##
============================================
+ Coverage        78%   78.28%   +0.28%     
- Complexity      333      341       +8     
============================================
  Files            23       23              
  Lines           800      815      +15     
============================================
+ Hits            624      638      +14     
- Misses          176      177       +1

Impacted Files	Coverage Δ	Complexity Δ
inc/TranslationApiRoute.php	100% <100%> (ø)	5 <0> (ø)	⬇️
inc/Project.php	100% <100%> (ø)	52 <4> (+4)	⬆️
inc/Updater.php	94.02% <85.71%> (-0.98%)	26 <3> (+4)
inc/ZipProvider.php	98.88% <0%> (+0.02%)	27% <0%> (ø)	⬇️

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