Display all other elements under "Elements" or "Assets" group.
Show properties for mjSpec, mjModel, and mjData for selected
elements.
PiperOrigin-RevId: 874614195
Change-Id: I128c2bec844983ac5d35a3a0b1e58b8a5b0109cb
This in preparation for an upcoming change that uses native file dialogs instead
of our very basic ImGui file dialog.
PiperOrigin-RevId: 861671041
Change-Id: I9b00c05efdda5e37ffe15048a2ccf66f6eca89d9