fix(@angular/cli): fix ng update for Yarn Pnp

[dominicbachmann]

Extend findPackageJson function to also work when using Yarn PnP

Fixes #26505

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

When trying to run ng update in a porject that uses Yarn PnP the cli does not detect the project dependencies because it cannot resolve the package.json paths.

Issue Number: 26505

What is the new behavior?

The cli resolves the package.json paths through .pnp.js when the project is using Yarn PnP.

Does this PR introduce a breaking change?

• Yes
• No

Other information

Not sure if this is a desired solution.

[clydin]

Thank you for the contribution.
It appears that Yarn PnP has an API available (https://yarnpkg.com/advanced/pnpapi). Would you be interested in converting this PR to use that?

[dominicbachmann]

@clydin Will do!