Support passing initial value for when creating documents

[HerbCaudill]

Why

Creating a document in a repo is currently a two-step process: First you create the handle -- at which point the type of your
document is a filthy lie, because its value is {} regardless of what you may have asserted. Then you have to use DocHandle.change() to set the various properties of your desired initial state:

const rootDocHandle = repo.create<SharedState>() // <- LIES!!!
rootDocHandle.change(s => {
  s.dones = []
  s.contacts = []
})

A better world is possible! One where this is done in a single step, and you don't have to endure that terrifying millisecond
without type safety.

How

When creating a new DocHandle with isNew, you can pass an initial value for the document:

const handle = new DocHandle(documentId, {
  isNew: true,
  initialValue: { dones: [], contacts: [] },
})

Similarly, when creating a new document with Repo.create(), you can pass an initial value:

const handle = repo.create({ dones: [], contacts: [] })