Add branch coverage stats to xml report

[chiefmyron]

Added new and elements under the element, and populated attributes appropriately. If path coverage is not enabled, the count, tested and percent attributes will all be set to 0.

I could not find a schema for the XML report to update / validate against (navigating to https://schema.phpunit.de/coverage/1.0 resulted in a 404 error).

Implements enhancement suggested in #1056.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.35%. Comparing base (b36a500) to head (f3b093f).
Report is 85 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1057      +/-   ##
============================================
+ Coverage     84.74%   85.35%   +0.61%     
- Complexity     1360     1364       +4     
============================================
  Files            90       90              
  Lines          4673     4705      +32     
============================================
+ Hits           3960     4016      +56     
+ Misses          713      689      -24     

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