Add a lot of flags to DesktopExperienceFlags.

As we already have a number of flags, if each individual dev tries to
add their flag to this file, this will cause a lot of merge conflict.
Instead, let's add them all at once, ready to be used.

Test: Build and run
Flag: EXEMPT (flag architecture)
Bug: 389092752
Change-Id: Idfbae45eab832252bbc0b88c39b6d5d981e600de