Improve file_length warnings when excluding comments

[g-mark]

This PR adds two minor tweaks to how file_length warnings are reported when ignore_comment_only_lines: true:

• Move warnings to the bottom of the file, rather than at the line corresponding to the abridged line count
• Adds "excluding comments and whitespace" to the warning when appropriate
  Old: "File Length Violation: File should contain 400 lines or less: currently contains 401 (file_length)"
  New: "File Length Violation: File should contain 400 lines or less excluding comments and whitespace: currently contains 401 (file_length)"

file_length warnings remain unchanged when ignore_comment_only_lines: false

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[marcelofabri]

Thanks!