remoting: Create composing capturer and mouse shape pump in pairs

DesktopCaptureOptions are used by both the mouse cursor monitor
as well as the desktop capturer. When composing the video with
mouse cursor, these two object rely on shared data in capture
options (e.g. shared X connection and shared screen cast for X11
and Wayland respectively).

In case of X11 implementation, there is currently only
one mouse shape pump that is used for all the video streams.
In case of Wayland, we have a single stream per capturer and it
makes sense to have a single pump for that stream. To that
end this change adds, a composer + cursor monitor manager class
to handle the differences in implementation between Wayland
and X implementation. This manager class will be responsible
for creating the condition video composer along with any
mouse shape pump needed with it. This new class is used by the
desktop environment class to create the composer (and implicitly
mouse shape pump / cursor monitor).

Bug: chromium:1291247
Change-Id: Ifd86bfae141aff46f831194ac7f2b886547dc6fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3857881
Commit-Queue: Salman Malik <salmanmalik@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1043957}