[Regulatory Labels] Load labels from overlays

When config_regulatory_info_overlay_package_name is configured, load
regulatory labels directly from overlay package.

Also fix RegulatoryInfoDisplayActivity missing dialog theme.

Bug: 283170651
Test: unit test
Test: manual - check regulatory labels
Change-Id: Ia1f6848abe0da9facf34f47abab09e88d57e74d6