General: gave MXMLBlockWalker the initial ability to output 'embedded' AS using the actual AS Walkers/Visitors/Emitters.

- created new "base" type for BlockWalkers and BlockVisitors, so methods can pass both AS and MXML versions around
- refactored existing BlockWalkers and BlockVisitors to implement these types
- MXMLBlockWalker now gets passed an ASEmitter and ASBlockWalker instance, which provide the actual AS parsing
- wrote some new MXML/FlexJS tests and made them pass with above modifications

git-svn-id: https://svn.apache.org/repos/asf/flex/falcon/trunk@1452890 13f79535-47bb-0310-9956-ffa450edef68