[Proposal-ish?] Lua should bind the Lua C API as a Lua module

["Soni \"They/Them\" L." <fakedme@...>]

Reading material:
https://en.wikipedia.org/wiki/Operating-system-level_virtualization
https://en.wikipedia.org/wiki/Protection_ring

Some game developers would significantly benefit from a slightly 
stripped-down[1] Lua C API as a built-in Lua module, as it would give 
the ability to create perfectly-isolated sub-states from Lua.

Because you'd be able to register (host) Lua functions as (guest) C 
functions, they'd appear as opaque C functions to the sub-states, which 
means the debug.* API could be trivially (and safely!) made available to 
them. For example:

GUEST | call os.time()
HOST | call guestostime()
HOST | <operations to implement the guest's os.time()>
HOST | return to guest
GUEST | get result created by host
GUEST | call debug.* functions against os.time, but get no useful 
results other than it being a C function.

It is technically possible to implement this in pure-Lua as it currently 
stands, at a hefty amount of overhead, both in terms of code/maintenance 
overhead, and CPU time. (it basically involves reimplementing the 
debug.* API by checking if the given function is a valid target for the 
debug API, and carefully wrapping host functions so they look like C 
functions to the guest, and so on.)

[1] - We don't want to expose luaL_newstate, we want lua_newstate to use 
the current state's allocator and stuff, and things like that.

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