Rename layout -> blueprint and add "sections"

Rename from layout to blueprint because layout is an overloaded word.
Items will not be components that we can use to determine our layout
constraints.
Also refactor blueprints to use multiple data layers for scalability.
Flag: MIGRATE_SPLIT_KEYGUARD_BOTTOM_AREA

Bug: 288464307
Test: Adjust tests and see that views in the rootview are properly
constrained.

Change-Id: I8369360614e100a37964cb869faa1a3acd694acb