Improve editor panning and remove RMB panning

[KoBeWi]

This PR does a couple of things:

• Improves cursor refreshing. Now _update_cursor() will automatically refresh the cursor shape if it's different from previous one (also fixes a regression from Request immediate refresh of cursor in 2D editor while using shortcuts #37336 where cursor would change even if not over 2D viewport)
• Pan View shortcut (Space by default) will automatically change cursor to CURSOR_DRAG while being pressed
  • Updated the panning mode tooltip to mention this shortcut
• Removes RMB panning, as it got in a way of properly using RMB in the editor (see Add tool quick-select to tile editor #51695 for example). We had 3 ways to pan view anyways

[groud]

I am in favor of this PR. I think having the right click available in the editor should allow several interesting thing, such as popping a context menu or do specific actions with some editors.

We need to pay attention to whether or not we have any complain about that though, I would not be surprised if it would annoy some users.

[sairam4123]

I am not favour of removing the RMB because it's difficult for me to pan around in the the 2D editor without it.

[KoBeWi]

@sairam4123 And what about Space panning? You can change it to any other key if preferred, there's also a setting called "Simple Panning" which allows to use this shortcut without LMB (like in GIMP for example).

[sairam4123]

That's pretty good then. LMB panning would really help.

[jordanlis]

I am in favor of this PR. I think having the right click available in the editor should allow several interesting thing, such as popping a context menu or do specific actions with some editors.

We need to pay attention to whether or not we have any complain about that though, I would not be surprised if it would annoy some users.

Totally agree with him : this features (right click -> menu) is totally missing. For example, it would be so usefull to right-click in the editor, then create a new node or instance a new scene at the mouse cursor's coordinates.
Like asked here : godotengine/godot-proposals#435

[akien-mga]

Thanks!