Add Pester v5 support to problem matcher

[fflaten]

PR Summary

This pull requests extends the problemMatcher pattern for Pester to support new timings printed by Pester v5+. This will enable vscode-powershell to also detect failed tests using a future release of Pester v5.

A related PR in Pester, pester/Pester#1700, is also required for this to work as it adds Pester 4-style output when tests are run in a vscode-task (not integrated terminal). This output is automatic and does not require the a special option like IncludeVSCodeMarker. The related PR will be released in Pester 5.1

Fix #2931

PR Checklist

• PR has a meaningful title
• Summarized changes
• PR has tests NA
  • Been tested with Pester 3.4.6, 4.10.1, 5.1.0-beta* (including PR). Tested using local change to package.json in 2020.6 extension
  • Verified that it still works with case resolved in Problem matcher support for Context errors #2447
• This PR is ready to merge and is not work in progress
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready

[TylerLeonhardt]

Thank you so much for this!