Remove Qt-specific code being split into glue-qt

[astrofrog]

This is part of #2430

• Rebase once Move frontend-independent data/link parsing code from glue.qglue to glue.core #2432 is merged
• Make sure that this works correctly with glue-qt
• Test that all downstream packages that don't need the Qt code work seamlessly with this version
  • glue-jupyter
  • jdaviz
  • glue-astronomy - with Fix compatibility with future glue-core changes glue-astronomy#95
  • glue-geospatial
  • glue-medical
• Add back compatibility imports for Qt with deprecation warnings

Packages that will need to be updated to use glue-qt wherever relevant:

• glue-plotly - see Generalize to work in glue-jupyter glue-plotly#41
• glue-solar
• glue-wwt - see Updates for glue-qt glue-wwt#98
• glue-vispy-viewers - see Updated imports to glue_qt glue-vispy-viewers#378

[dhomeier]

doc/conf.py:6:1: F401 'sys' imported but unused

also keeping the tests from running

[Carifio24]

I think glue-wwt should be in the "needs updating" list as well, as it has some Qt-based glue imports.

[dhomeier]

Tests for glue-jupyter are passing with this version and no Qt installed (except for those requiring glue-vispy-viewers, which cannot be installed without PyQt).

[astrofrog]

@dhomeier - hmm good point about glue-vispy-viewers - I think we should probably move the 3D state objects out of glue-vispy-viewers and into glue-core since they should be reasonably generic, and then we could depend on that instead of glue-vispy-viewers in glue-jupyter.

[dhomeier]

except for those requiring glue-vispy-viewers, which cannot be installed without PyQt).

The depency is only on conda-forge though; with pip-installed glue-vispy-viewers the other tests are passing as well...

[astrofrog]

I think the thing is that glue-jupyter does depend on glue-vispy-viewers for the 3D volume rendering viewer but we just haven't declared the dependency. However we should be able to refactor things to not have that dependency at all. I think I will delay this until after glue-core and glue-qt are split.

[astrofrog]

I'm going to go ahead and merge this as I think it is ready. I will also merge glue-viz/glue-qt#1 shortly. I will then do a release of glue-qt and add it as a dependency in glue-core so that glue-core should then continue to function as before just with deprecation warnings being raised now when Qt-related functionality is accessed.