Remove middle click shortcut to open scene tab

[KoBeWi]

When you middle-click in the scene tab TabBar outside any scene tab, it opens a new tab. I never found this useful and actually it constantly gets in my way. Every day I create a few empty tabs due to missclicks or editor lags while trying to close a tab.

Not sure if anyone relies on this function. You can still open a new tab by double-clicking on the tab bar. Or with the + button. Or with the shortcut. Or via filesystem dock.

EDIT:
Fixes #37055

[Calinou]

For reference, Firefox 104 has a similar middle-click behavior on empty space, but not Chromium 103. Neither have a double-click behavior on empty space though.

Either way, I'm fine with this change – I never rely on this shortcut personally (I only use middle-click to close tabs).

[akien-mga]

Let's give it a spin and see if it breaks someone's workflow.

[akien-mga]

Thanks!