NumberSpinner grabs focus on mouse wheel event

Steps to reproduce

When scrolling with the mouse wheel over an unfocused number spinner it grabs focus and the value is changed by scrolling through the available numbers.

This is problematic when using the mouse wheel to scroll a long form and the cursor passes over a number spinner.

Then the number spinner starts scrolling instead of the form, which leads to a value change in the spinner.

1. Add an integer property to a page (e.g. Standard page)
2. Go to "all properties" mode and resize the window so you get scrolling in the form area.
3. Scroll the form and let the cursor pass over the spinner input

Reported as a bug in dijit

https://bugs.dojotoolkit.org/ticket/18300