Support the new JUnit XML format.

[ericsnowcurrently]

(for #6990)

The JUnit XML format used by pytest was updated in version 5.1.0. This PR adds support for that format, and falls back to the old one.

This branch builds on PR #7263 and includes the actual fix for #6990. Please review commits after e58922a.

• Pull request represents a single change (i.e. not fixing disparate/unrelated things in a single PR)
• Title summarizes what is changing
• Has a news entry file (remember to thank yourself!)
• Appropriate comments and documentation strings in the code
• [ ] Has sufficient logging.
• [ ] Has telemetry for enhancements.
• Unit tests & system/integration tests are added/updated
• [ ] Test plan is updated as appropriate
• [ ] package-lock.json has been regenerated by running npm install (if dependencies have changed)
• [ ] The wiki is updated with any design decisions/details.

[codecov-io]

Codecov Report

Merging #7265 into master will increase coverage by 0.69%.
The diff coverage is 53.33%.

@@            Coverage Diff             @@
##           master    #7265      +/-   ##
==========================================
+ Coverage   57.99%   58.69%   +0.69%     
==========================================
  Files         494      494              
  Lines       21472    21838     +366     
  Branches     3493     3503      +10     
==========================================
+ Hits        12452    12817     +365     
+ Misses       8221     8220       -1     
- Partials      799      801       +2

Impacted Files	Coverage Δ
src/client/testing/common/xUnitParser.ts	62.5% <53.33%> (-3.61%)	⬇️
...t/datascience/jupyter/jupyterDataRateLimitError.ts	100% <0%> (ø)	⬆️
src/client/formatters/serviceRegistry.ts	100% <0%> (ø)	⬆️
...lient/datascience/jupyter/jupyterSelfCertsError.ts	100% <0%> (ø)	⬆️
src/client/debugger/extension/serviceRegistry.ts	100% <0%> (ø)	⬆️
src/client/common/variables/serviceRegistry.ts	100% <0%> (ø)	⬆️
src/client/common/process/serviceRegistry.ts	100% <0%> (ø)	⬆️
src/client/common/dotnet/serviceRegistry.ts	100% <0%> (ø)	⬆️
src/client/linters/serviceRegistry.ts	100% <0%> (ø)	⬆️
src/client/interpreter/serviceRegistry.ts	100% <0%> (ø)	⬆️
... and 27 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9f69bf7...d523f13. Read the comment docs.