Refactor comment_processable_test to not use so many mocks. (#2346)

Refactor comment_processable_test to not use so many mocks.

Now the only mock is the file system, and the MockSdk. This does make the tests
slower (re-analyzing the mock SDK each go), but they're certainly cleaner.

Also move more tests from end2end, mostly @animation and @inject-html tests.

Author: srawlins

pubspec.yaml

@@ -32,7 +32,6 @@ dev_dependencies:
   glob: ^1.1.5
   grinder: ^0.8.2
   http: ^0.12.0
-  mockito: ^4.1.1
   pedantic: ^1.9.0
   test: ^1.3.0