This is in preparation for lowering monomorphic loads during graph building.

This essentially moves the parts that will be shared to a separate class/file
(proparty-access-builder.(cc|h)).

I should say that we will not want to do accessor inlining during graph
building because that would require us to create frame states
(which is the thing we would like to avoid doing).

Review-Url: https://codereview.chromium.org/2936673005
Cr-Commit-Position: refs/heads/master@{#45973}