Use config_imeDrawsImeNavBar

With this CL, IME and SysUI start checking

  config_imeDrawsImeNavBar [1]

instead of

  config_navBarInteractionMode

when determining whether the IME should render the back and IME
switcher buttons or not.

There should be no observable behavior change as long as

  config_navBarInteractionMode

is set to true when the gestural navigation is enabled.

 [1]: I0651a99b6007a84be63b85b579a85af0f24bb6ec

Fix: 216118048
Test: manual
Change-Id: Ifdfd23612f6cb2bfe6ddf302e3caac1e342a8a1e