Read pointer choreographer flag at boot

In native code, we are sometimes reading the
enable_pointer_choreographer flag value at boot, and sometimes later
during runtime. Since DeviceConfig flag values can change at runtime,
the flag values loaded later can sometimes change, resulting in an
unexpected state where some code relies on the boot-time value and
others on the "current" value.

While we should have been using read-only flags in the first place, we
cannot convert existing flags to be read-only. So to increase
consistency within native code, change all reads of the
enable_pointer_choreographer flag to happen at boot.

This CL also updates the test to match the change in flagging approach.

Bug: 324534774
Test: Presubmit
Change-Id: I32cd6e52e2df260afd3d7681760a987ed060321a