Add a config resource to enable translucent bars globally.

Setting config_enableTranslucentDecor to false will not
prevent clients from adding FLAG_TRANSLUCENT_NAVIGATION or
STATUS to the window or using the TransluentDecor themes,
but it will prevent View.STATUS_BAR_TRANSLUCENT and
View.NAVIGATION_BAR_TRANSLUCENT from being propagated to the
SystemUI so these requests will not be honored.

Bug: 11182618
Change-Id: I8be6a3a565acf0987ff12f18f1c7e67c96d563c3