Rename Bonsai Viewer build option

Replace the old IFC viewer build switch with BUILD_BONSAIVIEWER in CMake, the Linux workflows, and the nix build script.

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src/ifcviewer/CMakeLists.txt

@@ -76,6 +76,6 @@ install(FILES ${IFCVIEWER_H_FILES}
     DESTINATION ${INCLUDEDIR}/ifcviewer
 )
 
-if(BUILD_IFCVIEWER_TESTS)
+if(BUILD_BONSAIVIEWER_TESTS)
     add_subdirectory(tests)
 endif()