Refactor to remove bytecode indirection

[jeffcharles]

Description of the change

Refactor to remove some indirection around how we get bytecode into the generator.

Why am I making this change?

As part of the PR implementing the RFC, I'm going to need to pass a PluginKind into the bytecode generation logic which kind of breaks the existing abstractions so I figure we may as well get rid of the indirection involved since it's not really adding any value.

Checklist

• I've updated the relevant CHANGELOG files if necessary. Changes to javy-cli, javy-plugin, and javy-plugin-processing do not require updating CHANGELOG files.
• I've updated the relevant crate versions if necessary. Versioning policy for library crates
• I've updated documentation including crate documentation if necessary.