Debug ID: Define how to extract `//# debugId=...` comment

[lforst]

Similar to how we defined an algorithm to extract sourceMappingURL comments in #94 we should define an algorithm to extract the debugId= comment.

• The same algorithm as for sourceMappingURL comments should likely be applied for debugId comments
• Should we define a separate abstract operation in the spec?
• Should adjust the existing algorithm to extract a "pattern" that is passed in? (pattern being either debugId or sourceMappingURL)
• Should we be more specific with regard to //@ since we don't carry historical debt? i.e. dissallow it for debugId comments?
• Should we define an algorithm for CSS too?
• We should add tests. Do we already have tests for sourceMappingURL?

[szuend]

We probably want a shared JavaScriptExtractMagicComment and CSSExtractMagicComment abstract operation. It can be parameterized so callers can specify whether a particular magic comment supports the legacy //@. Then we could disallow it for debugId.