Restructure repository layout

[dgp1130]

Since starting the repository I think I have a better understanding of how it should be laid out. I propose:

• //tools/binaries/... contains all the individual tool implementations.
  • Also includes the renderer, even thought that's technically not a standalone tool as the entry point is generated on each invocation.
• //packages/... contains individual @rules_prerender/* packages.
  • Code currently under //common/... should also be included here, and exporting a linked npm_package() though it would be listed a private: true in the package.json.
• //prerender/... contains all the Starlark definitions, mostly aligning with the way Aspect repos organize things. I think this will avoid pulling in unnecessary dev dependencies into user workspaces if no BUILD file load()s such a dependency.

Probably some other smaller changes to consider like the difference between an example and an e2e test, but we'll start with these changes.