Update input event tutorial to reflect recent changes

[Sauermann]

This PR updates the InputEvent tutorial

• resolve _unhandled_key_input method missing from documentation #2581
• resolve The InputEvent graph is outdated #2619
• resolve Outdated "How does it work" tutorial about Input Events #3369

Update input event flow graphic to reflect the changes of

• Fix unrestricted mouse-event propagation to SubViewports for Physics-Picking godot#57894
• Make SubViewportContainer event propagation aware of focused Control godot#79248
  Made some descriptions more precise.

Input Event table:

• Added missing InputEvents Gesture, MIDI and Shortcut
• Removed unused Type Index column

Updated 2023-08-05: include 4.2-changes

[Piralein]

Note for merge: the upstream PR is not marked for cherrypick-4.0 and has to be considered 4.1 documentation.

[mhilbrunner]

@Sauermann Seeing the first PR got merged and included in 4.1, and the second one at this point will be 4.2+, does it make sense to merge this and cherry-pick to 4.1, then do another one if further changes are needed for 4.2+?

[Sauermann]

@mhilbrunner That idea makes sense with respect to the content of the article.
However godotengine/godot#79248 will make it necessary to update the graphic again, which was my reason for waiting in order to keep the git-history small.

[Sauermann]

The other PR has been in circulation for two weeks now and got some testing. So I believe, that it is unlikely to be reverted.
I have updated the PR with the necessary changes for that PR.

[mhilbrunner]

We can wait a bit more then merge. LGTM.

[mhilbrunner]

@Sauermann Merged, thanks for all this work! I guess for 4.1 a separate PR is easiest, backporting the relevant parts?

[Sauermann]

Yes, that sounds about right.