Revive volume up/down long press in TV

PhoneWindowManager.interceptKeyBeforeQueuing isn't good place
to handle long press because rejecting a down event will not
synthesize further key repeat.

Move the logic to PhoneWindowManager.interceptKeyBeforeDispatching
instead.

This is the regression caused by following CL
001c59c6 Route volume keys directly to the audio system on TVs

Bug: 26268032
Change-Id: Ic8f6dfaec473c0d45ffa42475763622dc700e635