[Phone Hub] Reset ping request OnFeatureStatusChange

This change has the PingManager observe the FeatureStatusProvider and
reset the ping timer whenever the FeatureStatus changes to anything that
isn't kEnabledAndConnected. This makes it so when the phone disconnects and reconnects, the Ping Manager won't trigger another disconnect
when the original timeout timer fires.

This change also refactors the ping manager unit tests.

Test: manually verified that ping timer resets by changing networks
Fixed: b/275092984
Change-Id: I7526377730958a64af17e98858b3a14a91cf3fd9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4373884


Reviewed-by: Jon Mann <jonmann@chromium.org>
Commit-Queue: Crisrael Lucero <crisrael@google.com>
Reviewed-by: Pu Shi <pushi@google.com>
Cr-Commit-Position: refs/heads/main@{#1123187}