AV Digestor correctly passes format to LookupContext

ActionView::Digestor now passes arguments correctly to
LookupContext::find method. This makes cache digests
respect the format option correctly.

FixtureFinder in tests also changed to reflect this.
Merge pull request #10337 from eimermusic/fix_template_digestor_lookup

Fix ActionView::Digestor to correctly pass format to LookupContext

Conflicts:
	actionpack/CHANGELOG.md