The lack of icon gizmo made it no longer possible to select Camera3D
nodes in the 3D viewport by clicking on them.
A new Camera3D icon gizmo was designed to be direction-neutral.
This avoids the issue that the previous icon gizmo had, since it was
always facing right.
This also adds icons for CameraAttributesPractical and CameraAttributesPhysical.
More saturated icons go better with the new editor theme.
These color changes only apply when using a dark theme.
The editor icon saturation can still be adjusted in the Editor Settings.
Setting the editor icon saturation setting to 0.77 should roughly match
the old icon saturation.
