move imagefilters into separate dir and flag for build.gn

Requires https://chromium-review.googlesource.com/c/chromium/src/+/1105062

Bug: skia:
Change-Id: I948056234efa57c0f727a61d5fb3258034de5199
Reviewed-on: https://skia-review.googlesource.com/135566
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Reed <reed@google.com>
26 files changed