Merged pnpm6 experiment into pnpm detector

[pauld-msft]

Pnpm6 has gone through a week or so of experimentation after being introduced with https://github.com/microsoft/component-detection/pull/1110 and has been validated to work as expected.

This pull request:

• removes the experiment
• merges the pnpm6 changes into pnpm detector, using the suggested format from this comment
• increments Pnpm detector version from 5 -> 6

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.16667% with 7 lines in your changes are missing coverage. Please review.

Project coverage is 76.3%. Comparing base (9c3b0d5) to head (bfd9c50).

Files	Patch %	Lines
...ion.Detectors/pnpm/PnpmComponentDetectorFactory.cs	93.4%	4 Missing and 1 partial :warning:
...ComponentDetection.Detectors/pnpm/Pnpm5Detector.cs	94.1%	0 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1145 +/- ## ======================================= + Coverage 76.1% 76.3% +0.1% ======================================= Files 255 255 Lines 11306 11298 -8 Branches 1135 1134 -1 ======================================= + Hits 8614 8622 +8 + Misses 2357 2344 -13 + Partials 335 332 -3 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[github-actions[bot]]

👋 Hi! It looks like you modified some files in the Detectors folder. You may need to bump the detector versions if any of the following scenarios apply:

• The detector detects more or fewer components than before
• The detector generates different parent/child graph relationships than before
• The detector generates different devDependencies values than before

If none of the above scenarios apply, feel free to ignore this comment 🙂