Rename BootImageInfo to BootclasspathFragmentApexContentInfo

Currently, it only contains ART boot image related information, i.e.
.art, .oat and .vdex files. However, follow up changes will extend that
to include other information from bootclasspath_fragment.

Bug: 177892522
Test: m nothing
Change-Id: I2b226131c0eccff0c739a18f265f90caa10a91d9