tww: Load offsets from custom_symbols.txt file

[Aelire]

What is this fixing or adding?

This makes it simpler to update the client in lockstep with the randomizer and for development, by copying or symlinking the custom_symbols.txt file. Since even unrelated changes to the asm setup can cause offsets to change wildly, this should reduce the number of offsets that need copy-pasted on every client change

The custom_symbols.txt included in this PR is from ap_2.5.1

I also have a version of this rebased on top of fix-duplicate-items if that's a better target branch but the changes are minimal

Let me know if this is interesting and I can rerun some testing to make sure this exact commit works, and/or send directly upstream if that's better

How was this tested?

not yet tested independently on this exact version, but used with other changes to test synced changes between the randomizer and the archipelago client; did 3-4 of the following process:

• Change randomizer and regenerate patch_diffs
• Generate iso with randomizer
• Copy custom_symbols.txt into here
• Start game and verify starting items are properly populated