ozone/wayland: fix race in wayland buffer fuzzer

Given the fuzzer and the test wayland server run on different threads,
the objects on the test server side can only be accessed after the
server has processed the requests and is paused (the same what
we do in unittests).

Thus, to avoid usage of unitinitalized values, explicitly sync
(pause, resume, paus) after operations that require the server
to process the requests.

Bug: 1274248
Change-Id: I98e6f41d32085622ca6418c2b67cb2cd626fe0ef
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3318898
Reviewed-by: Alexander Dunaev <adunaev@igalia.com>
Commit-Queue: Maksim Sisov <msisov@igalia.com>
Cr-Commit-Position: refs/heads/main@{#948892}