Fix type inferencing, syntax highlighting and content assist for `enum` static initializers

[eric-milles]

Consider the following:

enum E {
  FOO, BAR, BAZ
  static final Set<String> NAMES
  static {
    Set<String> names = []
    names.add('foo')
    names.add('bar')
    names.add('baz')
    NAMES = Collections.unmodifiableSet(names)
  }
}

[eric-milles]