[lexical] Feature: error checking for node key re-use with type mismatch in __DEV__

[etrepum]

Description

Based on issues that several people have run into, it seems useful to add some additional invariant checking around node keys.

See also: discord message

• Adds a stub implementation of shared/invariant for use under jest to make development easier
• Adds a __DEV__ check to make sure that if a new Node is created with an explicit existing key, that the type of the node did not change

Test plan

Before

Bad things will silently happen if you accidentally re-use node keys, such as with a subtly incorrect node replacement function:

const config = {
  // ...
  nodes: [
    EdifactTextNode,
    {
      replace: TextNode,
      with: (node) => {
        return new EdifactTextNode(node.text, node.__key)
      },
    },
  ],
}

After

An error message is shows up now, in __DEV__. There are unit tests that verify that the specific error message comes up when creating a new node in this way (tested in isolation and with a node replacer).

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Name	Status	Preview	Comments	Updated (UTC)
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[acywatson]

I have a small concern about the size here - would be nice to be able to tree-shake this stuff out of the prod build.

[acywatson]

I have a small concern about the size here - would be nice to be able to tree-shake this stuff out of the prod build.

Discussed offline - we'll follow up and ensure that we're doing what we can to shake out these DEV things in rollup

[etrepum]

Just for posterity's sake I did confirm that unused functions that do not get exported are tree-shaken correctly in both the .mjs and .js prod builds at this time. Had this functionality not worked, it would also show up elsewhere (e.g. handleDEVOnlyPendingUpdateGuarantees is only used under __DEV__ in LexicalUpdates.ts)