Poor error recovery when typing an annotation at the end of a class body

[bwilkerson]

Given a file with the following content:

class Foo {
  @Export
}
class Export {
  const Export();
}

the annotation at the end of the class Foo will be discarded when using the analyzer. There isn't currently any place to hang this annotation in the AST, but we need to create one.

I don't know whether the parser will generate the necessary callbacks to capture the information, but if not then it needs to be fixed as well.

This impacts users when attempting to type an annotation before a soon-to-be-added member, and causes code completion to replace the wrong range of characters when it's used.