Rearrange the Element interface to match the many specs
Rearrange the Element interface to match the many specs

https://dom.spec.whatwg.org/#interface-element
and many other specs with partial Document interfaces.

To make reviewing easier, this commit only changes the order of lines
and adds comments. Actual spec sync will be done separately.

The order of the generated code changes, but there are no actual
changes.

BUG=460722

Review URL: https://codereview.chromium.org/970553002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@191056 bbb929c8-8fbe-4397-9dbb-9b2b20218538

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk