report: match all occurrences instead of the first one

[camshaft]

Problem

Currently when citing a text that appears multiple times in a section, it will only consider the first occurrence as covered:

//= my-spec.md#section-1
//# Text is here.

# Section 1

Text is here.
Text is here. <- not covered

Solution

Without any way to disambiguate between which text the implementation is referring to, text matching should instead be applied for all occurrences of that text. Later, we could also introduce a mechanism to specify which, if needed:

//= my-spec.md#section-1
//= occurrence=2
//# Text is here.