TreeInformation: sort via `const&` parameters
GCC 4.8.5 complains, but it feels actually more correct as the ability to modify already-sorted items probably causes all kinds of fun behaviors in the sort algorithm.
Fixes: #18833 (closed)
Cc: @mwestphal @BlueKnight7 @julien.fausty
Backport: paraview/release:HEAD^2^2
Backport: release:HEAD
Edited by Ben Boeckel