[SettingsProvider] minor refactor before lock changes

The old peekSettingsStateLocked lazily creates the config table on boot,
but it confuses a read-only method and a write method, which makes it
difficult to refactor SettingsProvider to use a ReadWrite lock. This CL
promptly initializes all the tables needed during boot and also during
new user creation. This is the preparation before introducing the
ReadWrite lock.

+ minor code style refactors

BUG: 284452689
Test: presubmit

Change-Id: Id57fb9dffd31be8438d2b7ba9714ac7bf4823302