Doxygen layout files are dependent upon doxygen version.  There
was a breaking change in 1.9.8 to support c++ modules.  Doxygen
groups had been labeled as modules, but are now labeled as topics.
- Renamed layout.xml to DoxygenLayout_1_8_10.xml
- Added DoxygenLayout_1_9_8.xml
- Add switch between the two based on the version of doxygen

This file causes the sidebar to disappear for Doxygen versions
1.10.0 and higher.
This file apparently only made cosmetic changes to the documentation,
so we will try not using it, rather than spend the time trying to
fix it.