Assign a category and policy to a license combination

**Note: the scope and details of this issue have changed since this original posting. See new comments below for more details.**

See related issue https://github.com/nexB/scancode-toolkit/issues/2897

We should assign a category+usage-policy to a license-expression to clarify license WITH exception cases.

It could be that all exceptions to a Copyleft license turn a license expression into a Copyleft-limited

It's important to clarify that the scope of this improvement is limited to "license WITH exception" cases and not more complex license expressions that express multiple licenses connected by the "AND" operator; that is, the "(license WITH exception)", ideally surrounded by parentheses, can be thought of as its own unit (a molecule?) and we can apply a category to that. Since the most common cases exist with the general rule that the category of the exception prevails over the category of the target license, we can make that the default behavior, but ultimately this should be controlled by SCTK detection rules to handle odd cases where that is not what is actually happening, for example, "exceptions" that simply tell you what you are allowed to do but don't really modify the target license terms.