Is your feature request related to a problem? Please describe.

Upstream Meshcat.js has the capability to use text as a texture. (See here for a demo.)

However, the Drake C++ Meshcat API does not offer any way to transmit the set_object message with those fields.

Describe the solution you'd like

Add another Meshcat::SetObject() overload to send this message. Something like:

 /** Sets the 3D object at a given `path` in the scene tree to the given shape
  whose material will be the given text (rendered onto canvas).
  The shape must be a primitive shape (not a mesh file). */
  void SetObject(std::string_view path, const Shape& shape, std::string_view text,
                 const Rgba& rgba = Rgba(.9, .9, .9, 1.));

Describe alternatives you've considered

Allow the user to give us arbitrary JSON for the object in a set_object and we could just pass that along.