Add global development setting to enable/disable vendor display settings.

(2/n)

This change introduces the DEVELOPMENT_IGNORE_VENDOR_DISPLAY_SETTINGS
setting which controls whether or not WindowManagerService should return
display vendor settings provided in the vendor/ partition. This will be
added as an entry in Developer Options to allow ignoring vendor settings
and using the default settings.

Test: atest WmTests:WindowManagerSettingsTests
Bug: 168808369
Change-Id: Iece0b76e4861be56186333134d7d5b25cab5c7e0