Fix aperture display in the inspector

Currently, aperture is just displaying a number (e.g. 2.0) whereas the
actual display format is "f/2.0"

This CL adds a small helper method to MediaView so that we can format
aperture correctly. Additionally, I updated the tests so that they check
for aperture display.

Bug: 64145689
Test: MediaViewTest.java
Change-Id: I553363ee4668889826eaad335855b917c35ab2da