Add tests for DisplayDeviceConfig

This CL can be reviewed patchset by patchset.

Patchset 1: test fallback to config resource
Patchset 2: test density mapping (only supported by DDC)
Patchset 3: move the density mapping test into a separate method, HBM data test (only supported in DDC)
Patchset 4: move the thermal brightness throttling data test into a separate method, fix the order of the methods
Patchset 5: test sensors
Patchset 6: rebase

Bug: 238992235
Test: atest DisplayDeviceConfigTest
Change-Id: I1910abb54b3bd8cb039615ef8a05706124df2126