Add a function to get tasks from multiple kinds in one pass

[glandium]

This is especially useful when some of the kinds the caller is interested in is a dependency of another kind.

[jcristau]

Would you mind adding a test for the new function?

[jcristau]

Suggested change

	Get all the tasks of a the given kinds.
	Get all the tasks of the given kinds.

[glandium]

Would you mind adding a test for the new function?

Adding tests unveils that the fake_loader here sets tasks.metadata.name to the name of the task without the kind, while the taskgraph on firefox-main would use the same as the label, so including the kind. Is that a purposeful difference? Because of course, without the kind, names are overlapping, so the result from load_tasks_for_kinds is incomplete.
But then maybe load_tasks_for_kinds should be changed to use the label instead of metadata.name?

[jcristau]

There seem to be other places where we assume the name matches the label e.g.

taskgraph/src/taskgraph/actions/retrigger.py

Line 150 in 6317207

label = task["metadata"]["name"]

; so changing the test fixture to set name to the same thing as label seems like a reasonable change, and would match

taskgraph/src/taskgraph/transforms/task.py

Line 1331 in 6317207

"name": task["label"],