Fix avm2 on `nat` branch

As is, `src/avm2/bin/avm.js` does not run on the `nat` branch. It expects two files in the build directory (`global.js` and `opcodes.js`) that do not exist, and refers to a different file (`genericVector.ts`) with the wrong capitalization (which works on Mac but not, e.g., on Linux).

This pull request fixes both these issues.