Rear displays should be considered presentation displays.

At the moment, we only want Presentations being shown on displays in the
rear position. In the future, even if we want to show more than just
Presentations, they're still an ideal target for Presentations so we
just implicitly make things with POSITION_REAR also have the
presentation category.

Also, rename position to device position. This is to avoid confusion
with display position, which is the position of the content on the
display device.

Test: atest LogicalDisplayTest
Bug: 267818951
Change-Id: I425add6fd0416ec2dc09c9ea721c0f24e4644d00