[meta2]: Improve meta2.closure.genArgsAliases

+ Add support for enums by emitting direct template argument references,
instead of aliasing __get__ functions. This makes captured enum values
usable at compile-time.

+ Make the implementation recursive in the case when a template argument
is an instance of Closure. This in effect expands such arguments to
their members. This should fix (or at least help trackdown) compilation
erros in more complex scenarios than the current unittest.

[meta2]: {WIP} Fix bug in meta2.closure

[meta2]: Add test for accessing closure members...

... directly using the with (closure) syntax.