Rather than duplicating code paths for in- and out-of-object stores,
have one code path which checks whether it needs to load the property
store (and change the storage location to the HeapNumber value for
unboxed doubles).

As a drive-by, change the representation dispatch into a switch, and
inline the representation checks into that switch, to make explicit
what checks for what and which paths transform the value. Also, TNodify
some of the surrounding functions.

Change-Id: Ia1bf698b4cec3ffce9aaa5732cda2e3be9efd8e8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1795345Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63652}