Lua profiler for nvim

[clason]

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One useful addition to a nvim-lua standard library would be a profiler (since the vim prof func * can't trace into lua). I've played a bit with the debug.sethook based approach, either using https://stackoverflow.com/questions/15725744/easy-lua-profiling or https://github.com/charlesmallah/lua-profiler.

Both kinda work, but it'd be nice to have something more nvim-aware (and prettier) :)

There's also https://blast.hk/moonloader/luajit/ext_profiler.html, but I couldn't get this to work properly.

[matu3ba]

Can you update the issue regarding what is missing from your merged PR to plenary? :)