ruleguard: associate rule line with a pattern string

[quasilyte]

In a multi-pattern rule, it's more useful to give a source line
of a respective pattern.

Consider this example:

     //line1: m.Match(
     //line2:        `foo()`,
     //line3:        `bar()`,
     //line4: )

Previously, if either foo() or bar() would match, we would
have a matchInfo rule line set to line1, since it's a
rule definition line (Match expression location).

Now we'll have a rule line set to line1 if foo() matches,
otherwise line2 if bar() matches. This is useful during
both debugging and rules usage.