Create a generator for `EmbeddedBuiltinDefinitions.cpp`

[tapple]

This C file is where slua gets its globals. slua-analyze won't work without it unless it grows support for d.luau files sometime soon

There's 2 places that would be really nice to typecheck, where including luau-lsp would be vastly overkill:

• slua playground https://slua-playground.wlf.io/
• the secondlife viewer

But, this is impractical without a generator for EmbeddedBuiltinDefinitions.cpp

[CatfishW]

/try

Plan:

• add a real EmbeddedBuiltinDefinitions.cpp generator path instead of another partial helper
• generate the full builtin source from both the Luau builtin section and the SLua/library section in slua_definitions.yaml
• emit a drop-in C++ file via a template, wire it into gen_all_definitions.sh, and add the generated output under generated/cpp/ for verification
• keep the existing slua_lsp_defs output stable while adding the new generator

[opirebot]

😅 Ups... this issue does not have any reward yet!