This patch implements the declaration of private accessors.
When iterating over the class properties, we track private
accessors associated with the same name in a ZoneHashMap.
Once we get to all the necessary components for a private name
(we know statically whether we should expect only a setter,
only a getter, or both), we emit a call to a runtime function
`CreatePrivateAccessors` that creates an AccessorPair, and
store the components in it. The AccessorPair is then associated
with the private name variable and stored in the context
for later retrieval when the private accessors are accessed.

Design doc: https://docs.google.com/document/d/10W4begYfs7lmldSqBoQBBt_BKamgT8igqxF9u50RGrI/edit

Bug: v8:8330
Change-Id: Ie6d3882507d143b1f645d7ae82b21b7358656e89
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1725670
Commit-Queue: Joyee Cheung <joyee@igalia.com>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63284}