Add security state API.

Adds API in android.os.SecurityStateManager. Currently the API provides
a method to get the global security state. This returns system SPL,
vendor SPL, mainline TVP SPLs, kernel version, WebView SPL, and SPLs for
security state packages defined in core/res/res/values/config.xml.

Design doc: go/dynamic-spl-api-design
Bug: 300984416
Test: manual

Change-Id: Ie1bcdb00adbd5495b2e4c812017c11b18fab7cf9