* CMake: use PROJECT_VERSION instead of solvespace_*_VERSION
In 006539b, solvespace_MAJOR_VERSION etc. were removed.
However, these variables were still referenced in some places.
Solution: Use PROJECT_VERSION instead.
* CMake: re-add link directories for solvespace target
006539b removed the call to link_directories for gtkmm, jsonc & fontconfig.
This leads to linking errors if those libraries are in "non-standard"
paths.
Fix this by introducing a target specific target_link_directories call.
Fixes#1173
* snap: port to core20 & adapt to CMake changes
Moving to core20 was long overdue anyway, and
the recent CMake changes necessitated some fixes.
Also switch to LZO compression for (way) better cold start
performance.
It was added in 3a3a2755b as a potential way to export colorful meshes
to Horizon EDA but ended up being supported only by SolveSpace. Since no
software can consume the exported q3do files the feature is superfluous.
See https://github.com/solvespace/solvespace/issues/795 for details.
Using gnome-3-34 gives us a newer stack in general
and also provides us with a sdk build-snap, so we don't need
to specify as many build-packages and stage-packages.
This makes the snap slimmer and delegates the responsibility
for security updates to the gnome platform snap for even more
packages.
As per https://snapcraft.io/docs/snap-layouts,
bind-mounts significantly increase the startup time of the snap.
Use symlink instead for better performance.
Remove all files from snap that are already included in the base snap
or in any connected content snaps.
The main advantage is the massively reduced snap size:
From ~70 MB down to ~6 MB.