Add frustum gizmo

[irate-devil]

Adds the FrustumGizmo which works in a similar fashion to the previously added AabbGizmo.

Closes #4082

Preventing cameras from drawing their own frustums made this a lot messier but as a result this is now technically the first retained gizmo q:

Here's a screenshot of a modified split_screen example showing the frustum of one view in the other.

Changelog

Added the FrustumGizmo component for drawing the frustums of cameras with the relevant settings added to the GizmoConfig resource.