Add @redwoodjs/project-model (+ Language Server)

[aldonline]

• Finalizing the work started by @peterp in this PR.
• Ultimate goal is to create a new package (@redwoodjs/project-model) that integrates what used to be decoupled/redwood-core

[aldonline]

I added a few eslint rule overrides.

• import/order - this is just for convenience, we can remove it eventually
• no-this-alias - this is necessary. some patterns (like using generator functions) require the const self=this alias
• no-non-null-assertion: this is necessary. there is a reason this assertion exists. especially when type-guards cannot be used (or require convoluted rewrites).
• no-case-declarations: supporting this rule would require rewriting most logic of the interactive_cli. I'm not opposed to doing that, but it doesn't add any value
• prefer-const: we could activate this rule eventually. there are some parts of the code that use "let" to allow quickly changing values when testing (by adding an extra assignment)
• no-unused-expressions: This gets in the way when using Wallaby.js

[peterp]

LGTM!