Code cleanup: Split DOM processors into individual files

Naming convention:
- dom.t.* are handlers that require a DOMTraverser to run
- dom.* can be run standalone

Other cleanup:
- Removed cached nodeType constants

No change in parser test results (as it should be)

Change-Id: I05532886c583686a76d5cd044feef2da4ea873d0
Merge "Code cleanup: Split DOM processors into individual files"