Fix the license field in various package.json

[frehner]

Closes #893

[github-actions]

We detected some changes in packages/*/package.json or packages/*/src, and there are no updates in the .changeset.
If the changes are user-facing and should cause a version bump, run npm run changeset add to track your changes and include them in the next release CHANGELOG.
If you are making simple updates to examples or documentation, you do not need to add a changeset.

[blittle]

Is it inappropriate to reference a file in the license field?

[frandiox]

@blittle Certain tools and websites pick this field to show the license automatically so it doesn't work well for us 🤔

[frehner]

@blittle See this comment for an example of what this looks like in npm #893 (comment)

[frehner]

npm's official package.json docs also recommend using the identifier:

If you're using a common license such as BSD-2-Clause or MIT, add a current SPDX license identifier for the license you're using, like this:
...
If you are using a license that hasn't been assigned an SPDX identifier, or if you are using a custom license, use a string value like this one:

{
 "license" : "SEE LICENSE IN <filename>"
}