ADIOS2 VTX Reader: Support any type of BP file
The reader was hard coded to only use BP3 or BP4. This changes to just use the generic "BPFile" engine, and let ADIOS choose the correct BP engine type based on the file. BP5 also requires using adios2::Mode::ReadRandomAccess
since the VTX reader doesn't use BeginStep/EndStep (and it's fine to use this mode option with BP3 and BP4).
Also fixes a CMake configure error in IOADIOS2 testing, where it failed when missing the Fortran component in ADIOS2, even though that's not required for testing.
addresses paraview/paraview#22108 (closed)