Support fully qualified and any relative requirement paths of a library's JavaScript

[nilmerg]

Is your feature request related to a problem? Please describe.

A library's JavaScript can require various dependencies by using define(). However, such a dependency is currently limited to:

• being located in the current library (no vendor dependency support)
• having no extension in its name (no extension other than js supported)

Describe the solution you'd like

• Vendor dependencies should be supported, i.e. dependencies which are unknown to the optimizer should be left alone
• Other extensions should be supported, js must still be the default