Improve Alpine package declared license detection

Technically Alpine packages declared license should be an SPDX license expression.
Yet in practice, things are messy and not always a proper license expression because of non-SPDX symbols or incorrect syntax.
The goal of this ticket is to improve the basic detection of the declared license in these cases including:
- create and use a mapping to actual scancode license expression for some cases that cannot be resolved otherwise
- apply transformations to the Alpine expression-like strings such that they become properly parsable expressions.