Always hides IME when launching Permission dialog activity

As the Permission dialog activity window is just a normal application
window rather than the overlay, even it will hide non-system overlay
window when it starts, but not including the IME window.

It could be covered by IME when the app was in multi-windowing mode that
IME z-ordering will be the top-most the display across apps window (e.g.
showing IME on split-screen in landscape mode).

As a result, it would be make more sense to hide IME always by adding
"stateAlwaysHidden" windowSoftInputMode in GrantPermissionActivity when
it launch.

Also add "adjustNothing" flag in case seeing the activity may flicker
by the activity being panned by IME insets  during launching.

And remove ALT_FOCUSABLE_IM flag by CL[1] to ensure windowSoftInputMode
flags takes the effect.

[1]: Ia6d761d6bdd5f3e759891d6da4efcbff8d6e4002

Fix: 265834504
Test: manual with below steps
    0) Request permission setup: choose any app (e.g. youtube) in
       Settings > Apps > App info. In "App permissions", choose
       Microphone permission -> select "Ask every time" to always launch
       permission dialog activity.
    1) Entering split-screen mode or ActivityEmbedings mode for the large
      screen devices (e.g. launch chrome & youtube app)
    2) In youtube tapping the search bar to show IME, then taping the
       mic. icon, expects the permission dialog activity is shown.
    3) Verify if the IME will hidden after dialog activity was shown.
    4) Press back key to dismiss the permission dialog activity, expects
       the IME will visible after focusing back to the youbute.

Change-Id: I7e09cd95d5f864e59cc8243780e0d4750f812336