This PR add pnpm full support

[farfromrefug]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the new behavior?

you can choose pnpm as the package manager

[rosen-vladimirov]

Hey @farfromrefug ,
Thanks a lot for the contribution. Can you please fix the linting error, so we can run some tests. Currently building of the package fails with:

ERROR: /home/travis/build/NativeScript/nativescript-cli/lib/package-manager.ts:104:9 - missing whitespace

[farfromrefug]

@rosen-vladimirov done. BTW for now i use --shamefully-hoist option for pnpm. We get to much errors without it. Might change that in the future if i manage to fix it.

[rosen-vladimirov]

test cli-smoke cli-templates

[rosen-vladimirov]

Hey @farfromrefug ,
I've tested your PR locally and it works awesome, great work! The only thing I've noticed is the command tns plugin remove <plugin name> fails with error. For example, in my case:

tns plugin remove nativescript-ui-listview
Command failed: pnpm remove nativescript-ui-listview --save
 ERROR  Unknown option 'save'

Can you please take a look at this issue? After that we can merge this PR.

[farfromrefug]

My bad! Will fix it this morning.

[rosen-vladimirov]

Hey @farfromrefug ,
Did you have a chance to take a look at the issue? If you want, I can try to take a look at it and push a fix

[rosen-vladimirov]

test cli-smoke

[rosen-vladimirov]

This PR implements #4654

[rosen-vladimirov]

Awesome work! Thanks for your contribution!