Add "Run tests" context menu option to package level test nodes #5953

Is your feature request related to a problem? Please describe.
We now have a toplevel node for tests of a specific Dart package.

Describe the solution you'd like
I'd like a way to "Run tests" (all tests of a specific project) from the context menu at that test node.

Describe alternatives you've considered
Going to the terminal and running from there.

Additional context

Normal test node:

Package node: