Rethink Activities button

Over the years we have observed a few issues with the current Activities button:

1. The word Activities hasn't always resonated with users, and in some cases has caused confusion.
2. In observations of people trying GNOME for the first time, users have either not noticed or not engaged with the Activities button. For some reason they haven't felt that it's the thing they need to click to launch apps.

We have been discussing this for some time, and the consensus on the design team is that the Activities label should be replaced with a more abstract visual element.

The latest concept for this is to convert Activities label into a dynamic workspace indicator. The latest prototype can be found in this shell extension: activities-filled-pill_verdre.zip