[Cast Receiver] Move RuntimeApplicationPlatform Interface to Component

This CL defines a new RuntimeApplicationPlatform interface to take the
place of RuntimeApplicationBase::Delegate as well as defining its
Client sub-interface to be implemented by RuntimeApplicationBase.
Additionally, the interface RuntimeApplicationDispatcher was moved.

Bug: 1359559, 1357135
Change-Id: Ib8c0bec624bd4e503af124ce46458b38424d2ad7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4027090
Reviewed-by: Vigen Issahhanjan <vigeni@google.com>
Commit-Queue: Ryan Keane <rwkeane@google.com>
Cr-Commit-Position: refs/heads/main@{#1073135}