[new AA] aaLiteral support

This PR depends on D-Programming-Language/druntime#933
This PR based on #3892, however in use zero AA init value.
I think, this way more pretty and safe.
New AA implemetation use template `object.aaLiteral` function to create AA.
This implemetation allows to return AA literals from CTFE, if `object.aaLiteral` can be evaluated at compile time. New aa implementation (D-Programming-Language/druntime#934) allow creating instances of AA at compile time (of cource, if hashes is CTFEable, and elements are eveluatable at compile time).
Template-based way implementation prevent using TypeInfo-based code, thus we need to know static Key and Value types to create AA instance.
As I said, this AA implementation doesn't use special initializer and empty AA like `int[int] aa;` doesn't know his static type.
When we try to insert value in AA, compiler generates call of a special function : `aaGetX` and if it takes `null` AA, it can't create new AA instance without auxilarity function.
Thus when compiler does it, it passes pointer to `aaLiteral(Key, Value)` (without arguments) to `aaGetX` and `aaGetX` can use this function to initialize empty AA.

> It creates a new AssocArrayLiteralExp object, sets keys and values to interpreted copies of old->keys and old->values, sets type to old->type and looks like semantic is done for the new object.

Yes, that's what I thought your problem is. This is correct because CTFE is done after semantics pass is done, so there is no need to recheck any types et.al.
The correct solution here is to rebuild the init expression in `scrubReturnValue`.