panel: Add workspaces indicators in activities button
After removing the app name and icon, the next natural step that was requested from the design team is to add workspaces indicators to the top bar, where currently the Activities button is placed.
In addition to that, this is desired because there are known issues with using "Activities" as a label for the overview. A more comprehensive rationale for that can be found at [1].
Add an workspaces indicator replacing the Activities label in the activities button.
The WorkspaceIndicators class controls how many workspaces dots exists, their expansion, and the width multiplier. The WorkspaceDot class takes the expansion and the multiplier, and applies it internally so that we can get perfectly rounded dots at all times without using CSS hacks.
The width multipliers are hardcoded, and defined by the design team. We can revisit them later if necessary.
When the number of workspaces changes, WorkspaceIndicators adds new dot to the end, and animate them. When removing, scale the dot out, then destroy it.
This does not work with workspace grids, but that's not supported by GNOME Shell anyway, so no effort is made to cover this use case.
The button continues to have "Activities" as its accessible name, but the label actor is removed.
Also adjust the padding of the activities pill, so it better wraps the new indicators.