[Fix #10734] Handle ClobberingError in Style/NestedTernaryOperator when there are multiple nested ternaries

[dvandersluis]

Style/NestedTernaryOperator was doing corrections by replacing the entire if node with a rewritten form. However, when there are multiple ternaries nested inside a single if, this caused a ClobberingError as subsequent rewrites would change the same range.

Instead, this takes a more surgical approach and edits by replacing the ? and : symbols and then wrapping the node with if/end. The result is the same syntax, but layout is no longer handled (but will be picked up by other cops).

Fixes #10734.

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• 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.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.

[bbatsov]

Nicely done!