[fuchsia] Create skeleton Inspect tree in each web_instance.

Create an Inspect tree, including nodes for each Context or Frame.
Publish the Chromium version information to the tree's root node.

base::ComponentInspectorForProcess() is removed, to avoid mistaken use
to add diagnostics directly to the process' Inspector root node.

base::GetKoid() is introduced, to reduce boilerplate required to obtain
the underlying KOID for a given kernel handle.

Some diagnostics are removed from OutputPresenterFuchsia, but it does not
appear that these could ever actually have been "visible" anywhere,
given the requirement to create the Inspect node before the Component
out-directory starts being served.

Bug: fuchsia:72819
Bug: 1128659
Change-Id: I0317f1748c4794ff0390781d3d7ce6ba77ab8533
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2882318
Auto-Submit: Wez <wez@chromium.org>
Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Commit-Queue: Wez <wez@chromium.org>
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#881704}