Export package.json from exports list in package.json to support introspection by build tools

[JimAllanson]

A common pattern in build tooling such as bundlers is to introspect the package.json file for dependencies. By providing an exports field in the package.json, external tools are prevented from being able to access package.json via require(), resulting in an error Package subpath './package.json' is not defined by "exports".

This change would add package.json to the list of exports, allowing it to be required in this manner.

This does appear to be some debate around this issue, and whether it's best solved by packages adding package.json to their exports list, by build tools being more robust against this scenario and falling back to e.g. fs APIs to read package.json, or even the suggestion that node itself should allow requiring of package.json without an explicit export. However, the pattern of adding package.json to the exports appears to be fairly commonly accepted.

Further context can be found here:
nodejs/node#33460
uuidjs/uuid#444
uuidjs/uuid#449

(In my specific case, I'm encountering this issue when trying to package a service that uses Apollo server for AWS Lambda, using esbuild with the Datadog esbuild plugin

[apollo-cla]

@JimAllanson: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

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