Framework: Per-block script bundles, server enqueues

[aduth]

Related: #2751, #4514, #2756

This pull request seeks to explore creating individual script bundles for each core block, reverting core registration changes introduced in #4514 while still separating core block registration from the underlying block APIs. The intent here is to work toward core block registration reflecting recommended block enqueueing, also laying a path for server-side block registration for core blocks (#2751) and eventually asynchronous block loading (#2756, #4500 (comment)).

Work-in-progress: The Webpack configuration has been updated to target each block, though could use some refinements particularly in how the global properties are assigned, and filenames of the build distributables generated. Only the paragraph block has been ported to being enqueued by the server-side editor_script handle property. Tests need to be fixed to register core blocks.

[gziolo]

I grouped all issues that we need to take into consideration when working on this PR under one column in the Extensibility project.

[kanishkdudeja]

I'm continuing work on this functionality. I haven't opened a pull request from my fork's branch to this branch yet. I'll do so once the work is nearing completion.

The diff can be viewed at the below link:

update/build-individual-blocks...kanishkdudeja:update/build-individual-blocks

[aduth]

It's unlikely this could be salvaged with changes made to master in the meantime. Going to close in favor of other pull requests, e.g. 6087 .