Move plugin `codegen` output to `./build` folder into a separate CLI command

[pileks]

Is your feature request related to a problem? Please describe. codegen for plugins appears to also output the plugins ABI into a ./build folder. This seems counter-intuitive, as the user expects the codegen command to only output to a codegen dir, and only codegen type definitions.

Describe the solution you'd like We should refactor this behaviour out into the polywrap build command, and extend the build command to support plugins as well.

• This would also move the --publish-dir option that the plugin codegen uses into build's --output-dir option
• codegen would then support wasm, plugin and app project types, while build would support wasm, plugin and interface types

Describe alternatives you've considered We can leave it as-is, but now that we have a unified codegen experience as part of #1051, I believe we should also move this build-like behavior into the build command.

Additional context We should also modify the plugin project template to reflect the new system of codegen/build commands for plugins.