This introduces a new builtin (MapLookupHashIndex) and uses it
in Turbofan to compute Map.p.get and Map.p.has.

I have also refactored the existing CSA builtins for Map.p.get and 
Map.p.has to use the new builtin under the hood.

The code for the lookup has been also improved.
- Specialized lookups for smis, strings, heap numbers and everything else.
  - the advantage is that we can use fast equalities for the lookup.
  - strings can likely be optimized further if we care about the 
    internalized string fast case.
- Instead of a call to runtime to get the hash code, we now call C directly.

In the Turbofan implementation itself, there are no special optimizations yet.
The next step is to teach load elimination to reuse the indexes from
previous calls of MapLookupHashIndex. 

BUG=v8:6410

Change-Id: I0b1a70493eb031d444e51002f6b2cc1f30ea2b68
Reviewed-on: https://chromium-review.googlesource.com/560169Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46510}