feat: disable "unused" warning for placeholders whose name starts with an underscore

[lars-reimann]

Closes #1154

Summary of Changes

Don't show a warning anymore that a placeholder is unused, if its name starts with an underscore.

[github-actions[bot]]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ MARKDOWN	markdown-link-check	1		0	1.0s
✅ REPOSITORY	git_diff	yes		no	0.17s
✅ TYPESCRIPT	eslint	2	0	0	4.38s
✅ TYPESCRIPT	prettier	2	0	0	0.93s

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[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (b469779) to head (7e04dcd).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1155 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 110 110 Lines 19201 19231 +30 Branches 4102 4110 +8 ========================================= + Hits 19201 19231 +30 ```

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[lars-reimann]

:tada: This PR is included in version 0.15.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• v0.15.0
• GitHub release

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