validate-npm-package - use node -e instead of npm compilation script

[le-cong]

use a better approach to import the main entry point based on the package.json

in order to simplify the implementation and align with our coding standards, we'll check only limited places inside package.json for determining the entry point:

{
  "main": "index.mjs",                            <-- here
  "exports": {
    ".": {
      "types": "./dist-types/index.d.ts",
      "import": "./dist-mjs/index.mjs",     <-- and here
      "default": "./dist-mjs/index.mjs"
    }
  },
}

error will be reported if no entry point is found in the above locations.

for the details of all the available options, please refer to https://nodejs.org/api/packages.html#package-entry-points

[le-cong]

@carlansley do you think we should check "main": "index.json" as well? or we should change whichever project currently using "main" to use "exports" instead?
allowing "main" is better for backwards compatibility and we could come back in the future to remove it to enforce more restricted checks.