Implement the unescaping of doc string delimiters

[stof]

Closes #326

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.86%. Comparing base (78aa8df) to head (09c8f65).
⚠️ Report is 2 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #393      +/-   ##
============================================
+ Coverage     95.83%   95.86%   +0.02%     
- Complexity      667      669       +2     
============================================
  Files            44       44              
  Lines          1921     1934      +13     
============================================
+ Hits           1841     1854      +13     
  Misses           80       80              

Flag	Coverage Δ
php8.1	95.86% <100.00%> (+0.02%)	⬆️
php8.1--with=symfony/yaml:^5.4	95.86% <100.00%> (+0.02%)	⬆️
php8.1--with=symfony/yaml:^6.4	95.86% <100.00%> (+0.02%)	⬆️
php8.2	95.86% <100.00%> (+0.02%)	⬆️
php8.3	95.86% <100.00%> (+0.02%)	⬆️
php8.4	95.86% <100.00%> (+0.02%)	⬆️
php8.5	95.86% <100.00%> (+0.02%)	⬆️

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[stof]

phpstan is smart enough to analyse the regex used to match the delimiter and figure out that the delimiter capturing group will only ever match one of the 2 supported delimiter strings.
Using a more precise type for the property in which we assign that value allows us to avoid a dead default branch in the match statement finding the corresponding escaped delimiter.

[stof]

this is where we had a mismatch compared to the upstream expectation.

[acoulton]

Great, thanks @stof