Dump more dex file data in oatdump

Dump some statistics for each dex file along side with strings loaded
from code and dex code bytes.

Sample output:
Cumulative dex file data
Num string ids: 202809
Num method ids: 320464
Num field ids: 162822
Num type ids: 68151
Num class defs: 48061
Unique strings loaded from dex code: 51049
Total strings loaded from dex code: 106651
Number of unique dex code items: 247929
Total number of dex code bytes: 11090574

Added content testing to oat dump test. No significant slowdown.

TEST: test-art-host
Bug: 29462018

Change-Id: I60effd3087d8c427eda4ee26431d5d77165b3939