layer-shell: Create/destroy layer_subsurface objects on parent map/unmap

Otherwise subsurfaces try to reach their already destroyed parents in their destroy handler, which can happen when the client destroys parent surface without destroying its subsurfaces first.

This mirrors the way subsurfaces are handled in views.

Closes #95 (closed)

not tested but looks good to me.

I'm beginning to test squeekboard with this.

@dorota.czaplejewicz any results yet? :)

I'd like to get this and !58 (merged) in and make a release to get new phoc into amber-phone.

I've only had to test a few times, but haven't noticed anything unusual.

Looks okay.

added 12 commits

• fb8defa2...5747ba2a - 11 commits from branch Librem5:master
• 5ec4b47b - layer-shell: Create/destroy layer_subsurface objects on parent map/unmap

Compare with previous version

If it looks so good, then let me squeeze it in... :)

merged