Add support for conflict directives in Lua modulefile like done for Tcl
modulefile.
Note that conflicts are correctly honored on Lmod and Environment
Modules <4.2 only if mutually expressed on both modulefiles that
conflict with each other.
Migrate conflict code from Tcl-specific classes to the common part. Add
tests for Lmod and split the conflict test case in two.
Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>
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