Setup Viz to Renderer mojo connections for input handling.

Browser was already brokering a connection between Viz and Browser for
RenderInputRouterClient interface. In this change we are setting up
following connections between Viz and Renderer using
RenderInputRouterClient interface:
- WidgetInputHandler: To send input events to Renderer.
- InputTargetClient: For asynchronous hit testing.

Following connections are not established between Viz and Renderer:
- FrameWidgetInputHandler: IME, text selection will not be handled by
  Viz.
- WidgetInputHandlerHost: Browser will continue to act as only host.

Bug: 370506271, 382291983
Change-Id: Ia168aa86ca560f259cc0b2b0fd90295df7e96d90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6073148
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Kartar Singh <kartarsingh@google.com>
Reviewed-by: Antonio Sartori <antoniosartori@chromium.org>
Reviewed-by: Stephen Nusko <nuskos@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1404587}