bugfix: screenshots now respect the `GLConfig` and contain a depth + stencil buffer when one is required (#3444)
fixes #3438
## What's new?
- `BasicScreenShooter` now respects the `GLConfig`
- When depth and stencil bits are provided, we create a render buffer
for them
I was unable to make separate stencil/depth buffers worked, but it is
_apparently_ recommended that they are combined. I don't know if this
will have any major issues...
feature: a test harness for window managers + tests for the MinimalWindowManager (#3416)
This PR establishes an initial test harness that is suitable for
`MinimalWindowManager`. We might need more harnessing for
`FloatingWindowManager`, but that should come as a follow up if we need
it.
## What's new?
- Built out the `WindowManagementTestHarness`
- Wrote some initial integration tests for the `MinimalWindowManager`