add build script for next-error-code-swc-plugin (#77931)
Adds a build script for `next-error-code-swc-plugin`, runnable via `pnpm
build-error-code-plugin`. The script compiles the plugin and moves the
result to its expected location in
`packages/next/next_error_code_swc_plugin.wasm`.
I've also rebuilt the plugin and committed it -- i was getting a
different compiled output that what's currently there. Not sure if the
build is non-deterministic, a dependency changed, or if someone forgot
to recompile it, but it can't hurt.
