Feature Request: support xparse-style declarations when auto-generating cwl

Currently, only latex2e-style declarations like \newcommand and \newenvironment are analysed in the process of auto-generating cwl files.

Nowadays, more and more new packages are (re)written using new declaration commands provided by xparse pacakge (which is based on latex3). Before the related cwl files are manually added into txs, maybe it is better to support xparse-style declarations at code level first.

A bnf-like description of these new declaration could be found here), and the first part is as follow

xparse-declare ::= cmd-declare <cmd name> arg-spec <definition code>
                 | env-declare <env name> arg-spec <begin code> <end code>

cmd-declare    ::= "\\" prefix ["Expandable"] "DocumentCommand"
env-declare    ::= "\\" prefix "DocumentEnvironment"
prefix         ::= "New" | "Renew" | "Provide" | "Declare"

arg-spec       ::= argument*
argument       ::= processor* [modifier] arg-type

Parsing <cmd namd> is not a problem, but counting the exact number of arguments may take some effort.

PS: I wonder if regex can parse > {\SplitList{,}} m to m, since it seems need a stack (to skip paired braces).

Start by locating the code that auto-generates cwl files and handles existing LaTeX2e declarations such as \newcommand and \newenvironment. Compare that entry point with the supplied xparse grammar, including nested brace handling and argument counting; done means xparse-style commands and environments are analysed correctly during cwl generation.