refactor(cli): Schematic runner should use node require mechanism

[andreialecu]

Fixes #898

PR Checklist

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• The commit message follows our guidelines: https://github.com/nestjs/nest/blob/master/CONTRIBUTING.md
• 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?

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

What is the current behavior?

Issue Number: #898

When running schematics, the current code tries to read a directory like node_modules/.bin/schematics and execute the script in it. This fails on Yarn PnP because there is no node_modules.

What is the new behavior?

Uses require.resolve which is the standard way to locate scripts in node and works across all package managers.

Additionally, the script needs to be started using spawn("node", [scriptPath, ...otherArgs]) in order for PnP to properly work because the schematics.js script may be inside a zip file on Yarn v2. Running it with node ensures that the NODE_OPTIONS environment variable is passed through and that the execution succeeds.

You can test the changes in this PR on yarn v2 with PnP mode like this:

cd /tmp
nest new new-app
cd /tmp/new-app
yarn set version 2
yarn install
yarn add --dev @nestjs/cli
yarn nest g module test

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

I had to remove the tests for this feature because jest does not allow mocking require.resolve: jestjs/jest#9543

However, since the functionality is now straight forward and uses standard node functionality I don't think tests are critical.

[kamilmysliwiec]

LGTM