Support new format ConTeXt LMTX and driver LuaMetaTeX

[hmenke]

Brief outline of the proposed feature

The current ConTeXt support and LuaTeX driver do not work with the new LMTX format because lots of primitives have been removed or renamed. It's likely unsustainable to add comptibility code to the LuaTeX driver so a separate LuaMetaTeX driver would be desirable.

[hmenke]

Related issues are #958 and #989

[ljrk0]

Thanks to the change by @hmenke at least #958 works again now (should that specific issue be closed?).

However, I've also noticed ConTeXt LMTX seems to be now shipping with a m-tikz.mkiv file with the following comment:

%D A fixed variant if [sic!] the t-tikz module distributed with tikz.

This overrides some catcodes and for LMTX also provides some other interfaces -- it seems to be not present in the MkIV distribution. Anyway, there seems to be some effort by Hans to keep this compatible. Reading the more recent ConTeXt mailinglist posts regarding TikZ there doesn't seem to be much awareness that these issues actually exist.