Support file name patterns (globs) to find files

Problem

Currently we only support exact matches on the file system and no globs as in https://rubyapi.org/3.3/o/file#method-c-fnmatch.

This prevents matching lib/api/issues.rb to spec/requests/issues/*_spec.rb.

The following configuration is currently not supported:

mapping:
  - source: 'lib/api/(.*)\.rb'
    test: 'spec/requests/%s/*_spec.rb'
  - source: '(ee/)?app/models/(.+)\.rb'
    test: '%sspec/models/%s/**/*_spec.rb'

Proposed solution

Use Dir.glob instead of File.exists? to allow the configuration above.

Performance consideration

Using Dir.glob is slower than File.exists? and we need to test the difference.