* On API 29+ we need the location permission to start the hotspot, while
on lower API levels, we don't. In order to handle permissions and
other conditions in a clear manner depending the API level of the
device the app is running on, have separate extensions of the base
ConditionManager class.
* Take special care to handle situations gracefully where the Wifi is
disabled and the user tries to start the hotspot. We cannot simply
rely on Wifi being enabled as a sufficient condition that allows us to
start the hotspot. We need to wait for WifiP2p to be available. While
it is tricky to obtain that state (it involves registering a broadcast
receiver for the WIFI_P2P_STATE_CHANGED_ACTION broadcast, keeping
track of changes there and even then things are still ugly. It can
happen that WifiP2p is available *before* Wifi is. Also it can happen
that WifiP2p never becomes available because some other application
has already opened a hotspot. Instead of checking that state, we now
just try (and retry repeatedly after a delay) to start the hotspot
(and the WifiP2p framework) hoping that is becomes availabe within a
reasonable amount of time after Wifi has been detected to be on.
Currently we try 5 times with a delay of 1 second.
* Improve the behavior of disabling and re-enabling the 'start hotspot'
button, so that it becomes impossible to double-tap it, but still
making sure that the button get re-enabled as soon as the UI is back
in a state where the user should be able to tap the button again.
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