Shares the feedback slot when loading / storing named properties
when the name of the property and the variable corresponding
to the object are the same. This reduces the memory usage on most
real world benchmarks. There is a slight (~1%) increase in the overall
time spent in V8 on a couple of these pages.

There is also no overall performance regression on peak-performance
benchmarks like Octane, ARES. More detailed results are in this doc[1]

[1]: https://docs.google.com/document/d/1rPNjXU-WOlyNQovuQS28Zf2PHCENR97Bi76gV9mHHOc/edit?usp=sharing

BUG: v8:7530
Change-Id: I7dd98c2d26f4e6c94690ca7d9a8a4a8281b3142d
Reviewed-on: https://chromium-review.googlesource.com/966302
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53145}