I messed up and released 40.alpha at the same time as 3.38.2, when it's
supposed to be in January. In order to re-align with the schedule, change
the upcoming version to 40.alpha2 so we don't have to skip a release and
will be back on track in time of 40.beta.
We kept the old binary name when overhauling the tool for the Extensions
app to avoid unnecessary churn for packagers/distributors.
However we now have a reason to "free" the old name, so rename the binary
to match the (sub)project name.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1220
The Extensions app code is now independent enough from the rest of the code
base to move it to its own subprojects, like we did for the extensions-tool.
This allows for stand-alone builds of the app, which we are about to use
for distributing it as flatpak.
https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1133
