[runtime] Store constructor function index on primitive maps.

[runtime] Store constructor function index on primitive maps.

This way we can greatly simplify the different variants of ToObject in
our codebase and make them more uniform and robust.  Adding a new
primitive doesn't require finding and changing all those places again,
but it is sufficient to setup the constructor function index when
allocating the map.

We use the inobject properties field of Map, which is invalid primitive
maps anyway.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1276533003

Cr-Commit-Position: refs/heads/master@{#30119}