[bt][common] Add WindowedInspectNumericProperty utility

Create time-bounded, or "windowed" inspect numeric property wrapper that
decrements itself when a value modification becomes stale.

Fixed: 70903
Test: fx test bt-host-common-tests
WindowedInspectNumericPropertyTest.*

Change-Id: If24dce441d09440e9933fe41eeda4254cfc1b158
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/490838
Commit-Queue: Ben Lawson <benlawson@google.com>
Reviewed-by: Xo Wang <xow@google.com>
Reviewed-by: Marie Janssen 💖 <jamuraa@google.com>