[UX] Soft transition modifier control settings for "Mouse wheel zooms by default"

Inkscape 1.1 has cool new modifier settings. But the transition is kind of rough since at least one previous setting that is ubiquitous is eradicated.

In response to #3608 (comment 454104576)

Summary:

1.1 deletes the setting "Mouse wheel zooms by default" because there's a new, powerful way to configure it.

I think it could try to convert the setting to the new scheme.

Steps to reproduce:

Set "Mouse wheel zooms by default" (Preferences (Edit > Preferences), then go to Behavior > Scrolling) enabled in an older version of Inkscape.

Get 1.1 alpha.

What happened?

Mouse Wheel does not zoom any more, requires CTRL modifier.

What should have happened?

Analyzing the old settings, The modifiers vertical pan and canvas zoom should have swapped:

Version Info:

- 1.1-alpha (bb1f551, 2021-01-30)

Warning

This would be a nice-to-have but messing with config files can be risky. Unless Inkscape has a way of ensuring that unexpected content in old config files doesn't mess up the new version's config file already, perhaps skip this.