Make extensions::DictionaryBuilder and extensions::ListValue unmovable.

There's no reason for these classes to be movable. std::move() is just
being used as a synonym for Build().

In addition:
- Build() is fewer characters than std::move().
- clang-format works better when builder syntax is consistently used,
  which makes it easier for readers to visually match up deeply nested
- It's surprising to see std::move() used with what looks like a


Review URL:

Cr-Commit-Position: refs/heads/master@{#378107}
93 files changed