gh-151949: Fix Sphinx reference warnings in `Doc/library/lzma.rst` (GH-153878)

gh-151949: Fix Sphinx reference warnings in `Doc/library/lzma.rst` (GH-153878)

The lzma module constants (FORMAT_*, CHECK_*, PRESET_*, FILTER_*, MODE_*
and MF_*) were referenced with the :const: role throughout the module
documentation but were never defined as reference targets, producing
"reference target not found" warnings under nitpicky mode.

Document these public constants with .. data:: directives, following the
convention used by the signal, socket and ssl modules, so the existing
references resolve. The now-redundant inline descriptions of the format
and check constants are condensed into linked references.