RFR: 8297554: Remove Scene.KeyHandler

[Ambarish Rapte]

On Thu, 24 Nov 2022 06:49:02 GMT, Michael Strauß <mstrauss at openjdk.org> wrote:

> The `Scene.KeyHandler` class doesn't seem to have a clear purpose, mixing focus handling with event propagation. Since #852, `KeyHandler.setFocusVisible` is also called from mouse and touch event handlers, which makes the purpose of the class even less pronounced.
> 
> Moving the focus-related functionality next to the other focus functions in the `Scene` class makes it easier to work with the code in the future.
> 
> With the focus-related functions gone, `KeyHandler` only contains a single, small method that is called from `Scene.processKeyEvent`. For simplicity, this code can be rolled into `Scene.processKeyEvent` and the now-empty `KeyHandler` class can be removed.

It looks in a quick look, shall review in detail in couple days.

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PR: https://git.openjdk.org/jfx/pull/962