[rush-lib] react to pnpm v7 local install path breaking change

[jeremymeng]

Summary

In pnpm v7, the format of local installation paths and the hashing algorithm used to shorten paths have been changed. It caused error described in #3652. This PR adds handling logic for pnpm v7.

Details

How it was tested

The code is tested using https://github.com/Azure/azure-sdk-for-js repository

Impacted documentation

[iclanton]

Can we just use the dependency-path package instead of duplicating its functionality?

[jeremymeng]

Can we just use the dependency-path package instead of duplicating its functionality?

@iclanton Good point. I made the change. As far as I know our repo doesn't have such cases that are impacted by the hasing change so I don't know how to test that. Also how do I test my PR in our repo? Previously I was just patching the js file under node_modules.

[iclanton]

You can test this change in your repo by running node <path-to-rush-lib-in-your-clone-of-rushstack>/lib/start <args>, or, if you're testing something that uses the caching features, use node <path-to-rush-in-your-clone-of-rushstack>/lib/start-dev <args>.

[jeremymeng]

You can test this change in your repo by running node <path-to-rush-lib-in-your-clone-of-rushstack>/lib/start <args>, or, if you're testing something that uses the caching features, use node <path-to-rush-in-your-clone-of-rushstack>/lib/start-dev <args>.

Thanks a lot! Tested with our repo on Linux/Windows.