Allow accessing package/module FQN with Module Scope Operator

Quote Andrej Mitrovic's comment (https://github.com/D-Programming-Language/dmd/pull/2256#issuecomment-20069143):
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Module Scope Operator -> The scope word there is significant. It means in the scope of the module, not in the actual module.

Look at the documentation:

$(H3 Module Scope Operator)
    ...
    The leading $(SINGLEQUOTE .) means look up the name at the module scope level.

That last part says everything: look up the name at the module scope level. It doesn't say "look up the symbol defined in the module."
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Right now `.std.stdio.writeln();` is properly accepted.