[Feature] Add a TwigManager

[titouanmathis]

This PR adds a TwigManager which:

• adds the studiometa/ui Twig extension
• adds the StringLoaderExtension extension (see https://twig.symfony.com/doc/3.x/functions/template_from_string.html)
• adds the djboris88/twig-commented-include Twig extension when WP_DEBUG is true
• adds comment to the rendered Twig template with the file name when WP_DEBUG is true
• adds an @svg alias to the <theme>/static/svg to easily include SVG files

To-do

• Add tests
• Update docs

[codecov]

Codecov Report

Attention: 28 lines in your changes are missing coverage. Please review.

Comparison is base (88a33ab) 61.34% compared to head (d98ea86) 60.09%.

Additional details and impacted files

@@             Coverage Diff              @@
##             master      #24      +/-   ##
============================================
- Coverage     61.34%   60.09%   -1.25%     
- Complexity      150      162      +12     
============================================
  Files             7        8       +1     
  Lines           388      421      +33     
============================================
+ Hits            238      253      +15     
- Misses          150      168      +18     

Flag	Coverage Δ
unittests	60.09% <15.15%> (-1.25%)	⬇️

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Files	Coverage Δ
src/Managers/CleanupManager.php	37.25% <100.00%> (+28.55%)	⬆️
src/Managers/TwigManager.php	0.00% <0.00%> (ø)

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[titouanmathis]

Obsolete.