Build: composer dependencies added to production build

This has come up in the past (see #13497 and #16399), and we had fixed it with #14900, by removing dependencies from the production `composer.json` when those dependencies were in fact shipped with the plugin, inside the `vendor` dir of Jetpack.

Unfortunately, we've lost that fix with the monorepo reorganization:
https://github.com/Automattic/jetpack-production/blob/9.4/composer.json#L14

@anomiex had mentioned that we could try Composer's `provide` property, see if it could solve our problem:
https://getcomposer.org/doc/04-schema.md#provide

Let's see if that can work for us, instead of having to edit `composer.json` during the build process.

Start with the production composer.json linked in the issue and compare the lost fix in #14900 with the current monorepo setup. Read Composer's provide property documentation and the related issues #13497 and #16399; done means dependencies already shipped in Jetpack's vendor directory are no longer added to the production build without editing composer.json during the build.

Written by the indexing model from the issue text.