compositor-drm: Split assign_planes() into separate file

drm_assign_planes() is called to separate views out and decide what will
be taken out for plane composition and what will be left for the
renderer to compose.

It calls drm_output_propose_state() in order to find a good
configuration, which itself has a number of helpers that it calls. Break
these out into a separate file.

Signed-off-by: Daniel Stone <daniels@collabora.com>
2 jobs for drm-backend-split in 1 minute and 48 seconds (queued for 1 second)
Status Job ID Name Coverage
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passed #383856
container_prep

00:00:34

 
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build-native-meson

00:01:14