Feature flags support in Chooser

A minimalistic replica of the SysUI feature flag infrastructure so the
app could both reuse some of the existing flag infrastructure (local
flag flipping) and have features controlled remotely (through
DeviceConfig).

Bug: 262578843
Test: Manual tests with some injected debug code and local flag flipping
Change-Id: If4be0cfce17e98b978966ea5172f85c5d406f833
8 files changed