Add debugging support for Lua

It would be nice to be able to debug plugins in Lua editor like for example Zero Brane Studio:
https://studio.zerobrane.com/doc-remote-debugging

This may require to either have lua as dll instead of static library inside exe or at least added luasocket multiplatform library into Aseprite exe so it is possible to start a debug session. Also require needs to be allowed to load moddebug extension

Start by reading the linked ZeroBrane Studio remote-debugging documentation, then inspect how Aseprite embeds Lua and handles require for plugins. Determine whether the work should use a Lua DLL, bundled luasocket, or moddebug support; done means a Lua plugin can start and use a debugging session from the editor.

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