support package "exports"

[jkowalleck]

currently only the main context is directly exported.
This means, that a Model for example needs to be required like

const { Models: { Component } }  = require('@cyclonedx/cyclonedx-library');

of as

const Component  = require('@cyclonedx/cyclonedx-library').Models.Component;

-> this requires a wider import than needed.

Feature request:

allow imports ala

const { Component }  = require('@cyclonedx/cyclonedx-library/models');

implementation:

utilize package.json's "exports" key. attention! have typing, web and node confugured properly for each sub path export.

additionally:

have a functional test that reads this data and tests that the mentioned files actually exist.