Remove final_blank_line style from Layout/TrailingBlankLines

[koic]

Follow up of #5463.

In EnforcedStyle: final_newline (default), the following are checked.

• Superflous trailing blank lines at end of file.
• The presence of final newline "\ n".

The above requirements to be checked by this cop are satisfied.

Thus this PR removes supported final_blank_line style which is unclear useful opportunity. This will cause the SupportedStyles to be one, so the style configuration will be removed from this cop.
Also change the test codes to leave the test cases of EnforcedStyle: final_newline (default) and indent it again.

See the discussion in #5463 for the background of this change.

---

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• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
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  and description in grammatically correct, complete sentences.
• Run rake default or rake parallel. It executes all tests and RuboCop for itself, and generates the documentation.

[bbatsov]

I'm fine with this change, but before we go forward I'd like to first check in someone using the other style to get an idea why (https://github.com/search?p=2&q=EnforcedStyle%3A+final_blank_line&type=Code&utf8=%E2%9C%93).

[koic]

That's exactly right.
I investigated .rubocop.yml using git blame in some repositories, but I could not find a definite change intention to EnforedStyle: final_blank_line.

I don't know the advantage of final_blank_line, but there may be some advantages to style of inserting blank line at end of line.

On the other hand, I confirmed the setting of .editorconfig during investigation.
https://github.com/bbatsov/rubocop/blob/v0.52.1/.editorconfig#L8-L9

The .editorconfig has trim_trailing_whitespace and insert_final_newline settings, which can be set like final_newline. But I could not find a setting highlighting the advantage of final_blank_line.

This is difficult to conclude. I don't know the advantage of final_blank_line. On the other hand, this conflicts with "Superflous trailing blank lines at end of file.", which is a role of final_newline.

[bbatsov]

Seems I found the history of this change here - #490

[koic]

Thank you for finding that discussion! 🙏
By leaving final_blank_line based on the historical background, it seemed that there was no confusion.
I think I will close this PR. WDYT?

[koic]

[IMO] Of course, since the source code as the artifact is more important than an editor setting in a manufacturing process, I think that new_blank_line should not be inherently preferred. Apart from that, I understand that this alternative style is a solution to the above linked discussion 😃

[bbatsov]

Yeah, definitely. Perhaps we need to extend the documentation of the cop to elaborate on this and shed some light on the second configuration option.