feat: Custom JSX runtime

[jmoseley]

Proposed changes

• Move to our own JSX runtime, that executes the tree directly
• Remove the need for resolve, components just return their final value directly, or pass it to their children if specified.

Further comments

This is a full rewrite of what we had, and requires that consumers of the lib use our JSX runtime (typescript docs). This should not be too much of a hurdle, and gives us full control of the rendering of the tree, and removes the dependency on React.

[jmoseley]

I imported the package into cortex-api to make sure it works, and it looks like things are functioning:

https://github.com/cortexclick/cortex/compare/jeremy/gensx#diff-8005314294b9a664e462bbeb614dfc306aefa7a4c1cd5d6994935879b304afc0R18

[EvanBoyle]

Few questions/comments, but things are looking good!

[EvanBoyle]

Let's go ahead and ship it. We can continue reving on the rest and figure out more about type safety as we experiment with LSP/compiler extension support.