Implement handling for MS PowerPoint Presentation Mode.

* Introduce a FullScreenWindowDetector to manage routines for updating the list of sources being application agnostic, inspired by FullScreenChromeWindowDetector.
* Introduce a FullScreenApplicationHandler to make a decision about changing window to share in application specific way, inspired by FullScreenChromeWindowDetector.
* Remove FullScreenChromeWindowDetector as redundant.
* Add FullScreenApplicationHandler for MS PowerPoint and Apple Keynote on MacOS.
* Add FullScreenApplicationHandler for MS PowerPoint on Windows.

Bug: webrtc:3852
Change-Id: I06507d929308e85b882b2f8210a025afef7f26a9
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/156020
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Reviewed-by: Justin Uberti <juberti@webrtc.org>
Reviewed-by: Wez <wez@google.com>
Cr-Commit-Position: refs/heads/master@{#29993}