Rename Camera2D offset_h and offset_v properties

[madmiraal]

As identified here and here, currently, Camera2D has an offset property, an offset_h property and an offset_v property. The offset property sets the viewport of the camera relative to its position. The offset_h and offset_v properties control the relative position of the viewport within the drag margins (when enabled).

This PR groups all the drag properties together in the editor and renames the following and their underlying methods and variables:

• offset_h -> drag_horizontal_offset
• offset_v to drag_vertical_offset
• drag_margin_h_enabled -> drag_horizontal_enabled
• drag_margin_v_enabled -> drag_vertical_enabled
• drag_margin_left -> drag_left_margin
• drag_margin_top -> drag_top_margin
• drag_margin_right -> drag_right_margin
• drag_margin_bottom -> drag_top_bottom

Part of #16863.

[madmiraal]

Rebased following merge of #44605.

[akien-mga]

Thanks!