AI 145911: ADT #1778786: tool to generate stubbed jar file.

AI 145911: ADT #1778786: tool to generate stubbed jar file.
  This is only a preliminary CL. More will follow but this is
  a good start, with the following caveats:
  What it does:
  - take an input jar, a list of includes, a list of excludes.
  - generate actual Java source for the filtered classes.
  What it doesn't do yet:
  - some more work on filtering inner elements (methods, etc.)
  - properly generate inner classes.
  - hide synthetic fields.
  - some classes body are missing
  - directly generate a stubbed bytecode/jar rather than source.
  I'll likely want to keep the source generator for debugging
  purposes or if we want to integrate with a build system instead.
  - classpath will be changed in the final CL to refer to the external
  ASM lib rather than the project. I need the source for debugging
  rigth now.
  - will review comments before submitting.
  BUG=1778786

Automated import of CL 145911