Add a corpus of test files

Bug: 142252770
Bug: 169137236
Bug: 169139756
Test: This (fuzzer)

Attempt to cover the types supported by AImageDecoder:
- jpeg (progressive and baseline)
- png
- webp (animated and non-animated)
  - should maybe include lossless, too?
- gif
- ico (embedded png and bmp)
- bmp
- wbmp
- heif
- various dng formats

These files are either already checked into CTS or Skia.

Change-Id: Ib227639bf8da75f0e8e31e216bc6d1371e24cb75