tex2lyx: improve module support

tex2lyx: improve module support

The current heuristics only considered modules with styles that defined
a searched command in their preamble, and only for commands/environments
that were defined in the document's preamble. This limited the module
support drastically.

The new heuristics also checks for commands coming from packages. If the
command is not (re-)defined in the document preamble, it checks modules
that provide a style with a matching LaTeXName, checks for their
requirements and matches those with the packages loaded by the document.

If no module provides a searched style, but we found modules that load
packages that are loaded in the imported tex file, and if those packages
are not auto-loaded by LyX anyway, we also load this module.

fixes: #11259, part of #8229