fix: improve error messages presented to the user

[EricCrosson]

This commit improves error messages presented to the user when encountering errors parsing JSON.

This required a bit of refactoring, since we were performing too much work up-front, and swallowing the helpful errors with a fallback (that stops looking for a lerna manifest and starts looking for an npm 7 workspace) that happened too late.

I took this opportunity to improve the representation of package.json manifests, which makes interaction with serde more ergonomic.

Here's an example of an error message when I remove the version property in a package.json file:

; monorepo pin --check
Error: Unexpected contents in "./packages/my-package/package.json"

I'm trying to parse the following properties and values out
of this package.json file:

- name: string
- version: string

and if the any of the following values are present, I expect
them to be a JSON object with string keys and string values:

- dependencies
- devDependencies
- optionalDependencies
- peerDependencies


Caused by:
    0: Unable to parse JSON from file '"./packages/my-package/package.json"'
    1: missing field `version` at line 103 column 1

cc @lifeiscontent

[louib-bitgo]

@EricCrosson extraneous the here

[EricCrosson]

Hot dog @louib-bitgo you are on fire catching these typos! 🌭 🌭 🌭

[EricCrosson]

Addressed in #192

[ocornoc]

I don't have any unique criticism, looks good!

[github-actions]

🎉 This PR is included in version 4.2.4 🎉

The release is available on:

• v4.2.4
• npm package (@latest dist-tag)
• GitHub release

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