cli: Add check:theia-extensions command

[sgraband]

What it does

The goal of this PR is to improve the existing theia check:dependencies script introduced in this PR. The existing script returns a list of all mismatching version numbers for all dependencies. While introducing two versions of the same dependency can always possibly introduce issues, this will be much more common for Theia extensions, than for other dependencies like loadash or rimraf. Thats why:

This allows to check for duplicate versions of theia extensions only.
Added the option only-theia-extensions to theia check:dependencies.
Theia extensions are identified via their theiaExtensions field in the package.json.
The check is running recursively as long as it finds Theia extensions.
The recursion was added to also display cases where more than 2 versions of a dependency might extist.
The advantage of this approach is that a shorter, but more important, list is returned.

Fixes #12572.

Contributed on behalf of STMicroelectronics

How to test

• Check out this PR and build with yarn
• Go to dev-packages/cli and run yarn link
• Checkout this example (or create any other example you would like) and run yarn link "@theia/cli" in its root
• Run yarn to see the output (this will run theia check:theia-extensions on postinstall)

The provided example has a few issues built-in:

• The test-extension requires a @theia/core version of 1.37.2 while the application depends on 1.38.0
• To test nested (and 3rd-party) dependencies the following dependencies where added
  • test-extension > test-extension-3 > @eclipse-emfcloud/modelserver-theia:0.8.0-theia-cr03
  • test-extension2 > test-extension-4 > @eclipse-emfcloud/modelserver-theia:0.8.0-theia-cr01
  • @eclipse-emfcloud/modelserver-theia:0.8.0-theia-cr01 depends on version 1.37.2 of @theia/(core|filesystem|process|variable-resolver|workpace)

So the result of theia check:theia-extensions should find the following issues:

• Different versions for @theia/(filesystem|process|variable-resolver|workpace) from the application and @eclipse-emfcloud/modelserver-theia
• Different versions for @theia/core from the application, @eclipse-emfcloud/modelserver-theia and test-extension
• Different versions for @eclipse-emfcloud/modelserver-theia from test-extension-3 and test-extension-4

Note that one of the versions will always be hoisted to the root node_modules version

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[sgraband]

@tsmaeder Would you have time to review this sometime this week or next week? Or should we find someone else to review this?

[tsmaeder]

Sorry, this fell off the wagon. I'll make some time tomorrow. That said, could you resolve the conflicts?

[tsmaeder]

The code looks fine and seems to do what it promises.