Removed JCTypeAnnotation

[Werner Dietl]

On a suggestion from Jon, I removed JCTypeAnnotation and instead use
JCAnnotation and the tree Tag/Kind to distinguish the annotation type.
The use of the "attribute" field for declaration annotations needs
more work, but everything seems to work out nicely.
The parser and other parts are cleaner thanks to this change.

Thoughts?
cu, WMD.

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