Move blocks and extensions, filters, plugins to a new plugin for blocks

[tobeycodes]

We are currently loading blocks from the theme. Blocks are not tightly coupled to a theme. We should be writing CSS in viewStyles rather than in the CSS of the theme. This is better for CWV when using a block based theme as the styles will not load if the block is not on the page.

This makes it far easier to build multiple themes that share custom blocks or when working on projects that have a design refresh and need to more easily update their frontend to match new designs

plugins/block-library would have the scaffold generation and any block related code