Change baselayout content id

Right now we use the id "content", which can easily be
confused with android:id/content. In addition, if other
layouts use "@+id/content" on a view and a base layout
RRO is applied (on Q and earlier, which admittedly
won't really happen), they won't be able to find that
view without using CarUiUtils.findViewByRefId()

Bug: 160725709
Test: Manually
Change-Id: Ief8c65fb91bcb25696b6a6ba06b36c2b7edfdac9
9 files changed