[new AA] aaLiteral compiler support

This is a dmd part of the new AA implementation. 
This PR depends on D-Programming-Language/druntime#1046 and uses new aaLiteral version (with arrays of keys and arguments)

With this pull:
Without this pull `core.internal.aa` isn't imported from anywhere. With this pull, when you compile one or many modules with associative array, compiler instantiates `aaLiteral`, which contains `import core.internal.aa;`. I think, if you inserts aaLiteral call without this PR, you will get the same result.
druntime tests are passed in both (with and without this pull) versions and that makes me think that the error in the DMD and it isn't related with this work,