Consolidate doc generation and fix next/prev links issue

[oandregal]

This Pull Request seeks to address two issues:

• Handbook: next/prev links do not follow the sidebar order #14794 by modifying how the data docs are regenerated we fix the next/previous links for the data section.
• Update API docs for packages automatically #14227 See first task: update handbook to use docgen.

Depends on:

• Add private tag to INSERTER_UTILITY_* constants #15423 so those symbols are not added to the docs.
• Update docs for selectors & actions moved to block-editor #15424 these symbols will be added back to docs with this PR, linking to the proper core/block-editor symbol.

[chrisvanpatten]

I wish there was more that could be done here to abstract some of this (so the docs tooling doesn't need to have specific package names and such hard-coded in) but given the amount of work likely required to accomplish that, this seems like a perfectly practical path forward.