Spinner: Mousewheel events should be ignored when the input is not focused

[s0By]

I know this is somewhat intentional feature and is really annoying when the page is being scrolled by a user and, when the mouse gets over the spinner input, the page stops scrolling and spinning event starts inside the input.

This must be controlled. I bet in majority cases you would want to use a mousewheel scroll only when the input is actually focused. To comply for everyone, this could be made as an option, something simillar to what was done 7 years ago here:

​http://btburnett.com/spinnertest/demos/spinner/mousewheel-disabled.html

I don't like to tamper with the solution and to keep overwriting the code as the version goes higher, good options could be included by original developers.

[Scott González]

PR: ​https://github.com/jquery/jquery-ui/pull/1794

[Scott González]

In a3b9129:

Spinner: Ignore mousewheel events when not focused

Fixes #15139
Closes gh-1794