[fuchsia] Add basic implementations of fidl::AsyncEventHandler

HLCPP bindings had a `set_error_handler` method on the `InterfacePtr`
but that's no longer available for `fidl::Client`. Instead, it takes
a `fidl::AsyncEventHandler` that has an `on_fidl_error` method as
well as methods for other events available on the `Protocol`. The new
API shape creates quite a bit of extra boilerplate for just adding a
closure or logging on fidl error (when a service is disconnected).

This CL adds two basic implementations, one that just logs an error,
and another that takes a callback.

Bug: 1351487
Change-Id: If6ba87f24751af8daafb54904652164eb47d9875
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4325064


Reviewed-by: Guocheng Wei <guochengwei@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Commit-Queue: Bryant Chandler <bryantchandler@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1118929}