Fix accessibility in action bars and add extra customization

Fix a bug where the content description of the big unified Home/Up
button was not getting set properly.

Add the ability to change the home-as-up glyph from ActionBar.

Add the ability to set a custom action description for the home-as-up
button, useful if the above functionality is used.

Bug 8548229

Change-Id: I0635799772c7234b68247dfc105dce7f11acda32