Doxygen not building the VPR Grid doc properly

[vaughnbetz]

https://docs.verilogtorouting.org/en/latest/api/vpr/grid/ currently gives an error:
doxygenclass: Cannot find class “DeviceGrid” in doxygen xml output for project “vpr” from directory: ../_build/doxygen/vpr/xml

I think either this class was moved or some part of its doxygen comment has become corrupted. @soheilshahrouz : did you make any changes to this file? Can you take a look?

[soheilshahrouz]

Fixed in #2887