Feature: default presets

[jakemac53]

There isn't a good way today (that I know of) to only run a subset of your tests by default.

It might be nice if the preset configuration had a toggle to select whether it was enabled by default. This would allow easy configuration for the default dart test behavior.

Today if you want to only run a subset of your tests by default you have to either put the others in a non-standard directory, or you can use tags to automatically skip certain tests by default.

One consideration of this is that it might be easy to not realize that all the tests aren't running, so I don't know if we should log a message or something mentioning the selected presets?

cc @natebosch

[natebosch]

Was there a particular repo where you hoped to use this feature? I'm trying to imagine a concrete case where this would be a better UX than skipping by tags.

Edit: The relevant discussion is https://github.com/dart-lang/site-www/issues/5215