Separate v8/v9 eslint configs

[ecraig12345]

The current eslint configs were made a couple years ago before the plan for v9 was finalized. Instead of having v8/v9 share a config, they should have separate configs.

What we have today:

• react: most of the rules for v8/v9
• react--legacy: extends react; the main difference is this config requires interfaces to be prefixed with I
• node: rules for node-based packages
• node--legacy: extends node but with I on interfaces