create a tasks-focused solution filter, and make repo tests more usable in VSCode

[baronfel]

This is some stuff carved off of #51765 to minimize the diffs.

• add a tasks.slnf alongside the other use-case-focused solution filters to make working in the repo easier for vscode developers
• slightly alter the TestFramework library project so that it doesn't blow up test discovery, so that vscode based devs can actually run tests in vscode
• add a capability to the TestProject system to make it possible to run targets other than build when testing and recording property values