Rename OnWheel to OnMouseWheel

[RumBugen]

Pull Request

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Summary

This PR renames the editor/widget mouse wheel callback from OnWheel to OnMouseWheel so it is consistent with the rest of the mouse event API and easier to discover in IntelliSense. It also updates existing internal overrides to use the new name.

Motivation & Context

I have done this to address the discoverability problem described in the linked issue. Users looking for mouse-related widget callbacks naturally search for OnMouse, but OnWheel did not follow that pattern.

Fixes: #4623

Implementation Details

I renamed the wheel event from OnWheel to OnMouseWheel, while keeping OnWheel as an obsolete compatibility layer that is still invoked from OnMouseWheel, so that existing overrides do not break immediately. I also updated the current overrides to use the new name. This was done intentionally to allow existing code to migrate without breaking everything, while guiding new code towards the clearer API name. If there's anything wrong with this approach, let me know and I'll change it.

Screenshots / Videos (if applicable)

Checklist

• Code follows existing style and conventions
• No unnecessary formatting or unrelated changes
• Public APIs are documented (if applicable)
• Unit tests added where applicable and all passing
• I’m okay with this PR being rejected or requested to change 🙂