Account for NPM being case-sensitive

[mealingr]

Although for NPM according to https://docs.npmjs.com/cli/v7/configuring-npm/package-json#name

New packages must not have uppercase letters in the name.

some old NPM packages exist that do have uppercase letters in their names

For example

This package
https://www.npmjs.com/package/Base64/v/1.0.0

Is different to this package
https://www.npmjs.com/package/base64/v/1.0.0

However at the moment they have the same Package URL i.e.
pkg:npm/[email protected]

This PR stops the NPM namespace and name validations from lower-casing so that instead we end up with the Package URLs
pkg:npm/[email protected]
pkg:npm/[email protected]

[jdillon]

Just for reference this is exactly why I think PURL should not have these sorts of transformations; package-url/purl-spec#38 and that case or char translations should not be part of the PURL specification types.

[stevespringett]

Thanks for identifying the issue and submitting a PR. Much appreciated.