add --no-bundle option for static code generation

[taylorcode]

protobuf.js version: 6.8.8

Using pbjs with the static-module target produces a single JS bundle that contains the code for all transitively imported packages. I don't see an option to disable this behavior?

This is not ideal even for browser use cases, because any packages that are imported in multiple .proto files will appear in the bundles redundantly.

It also looks like they will clobber themselves at runtime, since the packages are attached to to $protobuf.roots["default"], e.g. $root.awesomepackage = (() => {. Any references to $root.awesomepackage would be destroyed once the code was redundantly loaded.

If bundling is desired, a tool such as rollup or webpack can be used by the consumer.