support multiple PHP_INI_SCAN_DIR's

[realFlowControl]

Description

In case a user sets the PHP_INI_SCAN_DIR environment variable to a special value with a leading or trailing : or has multiple directories separated by the default path separator, we need to handle this accordingly.

In case they use the trailing or leading : to just add or prepend to the default directory, there is no way for us to find that original value anymore, so we "just" always use the first explicitly defined path.

This is documented upstream at https://www.php.net/manual/en/configuration.file.php#configuration.file.scan

Thanks @rp-thomas for reporting

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.97%. Comparing base (7b487bd) to head (dcf645a).
Report is 1 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (7b487bd) and HEAD (dcf645a). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (7b487bd)	HEAD (dcf645a)
tracer-php	12	11

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2941      +/-   ##
============================================
- Coverage     82.10%   73.97%   -8.13%     
  Complexity     2527     2527              
============================================
  Files           108      108              
  Lines         10360    10360              
============================================
- Hits           8506     7664     -842     
- Misses         1854     2696     +842     

Flag	Coverage Δ
tracer-php	73.97% <ø> (-8.13%)	⬇️

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see 8 files with indirect coverage changes

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[bwoebi]

Looks good, thanks.