Add gamedata for sourcemod

[kassibuss]

Would let plugins to be created for the game

[Rainyan]

Rehashing some thoughts from the Discord discussion so they don't get lost:

We probably want to automate this, since we have symbols available obviously.

Possible leads to investigate to avoid reinventing too many wheels:
https://wiki.alliedmods.net/Signature_scanning
https://github.com/alliedmodders/sourcemod/tree/master/tools/vtable_scanner
https://github.com/alliedmodders/sourcemod/tree/master/tools/ghidra_scripts
https://github.com/alliedmodders/sourcemod/tree/master/tools/ida_scripts
https://github.com/microsoft/microsoft-pdb
https://www.akkadia.org/drepper/dsohowto.pdf

But if no convenient tool already exists for doing this kind of a thing, either:

• Write one ourselves
  • Could be nontrivial, but would save the effort of manually patching in the long run.
  • Although if it turns out to be too much work to be worth it, consider option B.
• Postpone until reaching semi-stable state in terms of signatures/offsets shuffling around; then write it manually once, and patch occasionally as needed
  • Similar to the closed-source gamedata situation of commercial Source games, although perhaps a bit of a waste, since we do technically have all the required info available for us in the build symbols for automation

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edit:
Since dedicated servers will most likely run Linux, it might also be acceptable to just provide the symbols as labels, like:
"linux" "@_ZN15CBaseTempEntity15s_pTempEntitiesE"
instead of signatures/offsets, as this should be relatively simple and stable, and leave the Windows symbols to be figured out at some later time.