* Create hdf5_1_12_2 preparation branch for HDF5 1.12.2 release.
Set version to 1.12.2-3.
Switch default build mode to production for release.
Switch AM_MAINTAINER_MODE to disabled.
Set HDF5_GENERATE_HEADERS to OFF.
Commit Makefile.ins and other generated files for release.
* Update so numbers.
Address codespell errors in files generated by autogen.sh.
* Populate "Support for new platforms section.