Super Dev Mode: remove -Xincremental and add new JobEvent properties

Removed -Xincremental which was the old incremental mode.
(We are going to use -XcompilePerFile in Super Dev Mode.)

New Job Event properties:
  - getArguments() returns the command-line arguments.
  - getCompileStrategy() returns an enum indicating if the compile
was full, incremental, or skipped.

Change-Id: I0606db5374faab778a46f3a90e6904f00917e6ce
Review-Link: https://gwt-review.googlesource.com/#/c/9100/