[new AA] implement aaLiteral

This functions will be used to constructing AA values: literals and nulls. When this PR will be merged, I will create PR for dmd, which uses this functions, and when dmd PR will be merged, I'll create PR, which rewrite this functions to use new AA implementation.
Use [`core.internals.traits.TypeTuple`](https://github.com/D-Programming-Language/druntime/blob/f888fbcff82f30c549a7cccd98191dedcc3101ec/src/core/internal/traits.d#L12).