fix: preserve blank lines when removing empty statements consistently

[utakotoba]

fixes #6816

Summary

Fix formatting around empty statements (;) so removing them does not break surrounding blank lines or comment placement. Before this change, rustfmt could behave inconsistently when an empty statement appeared by itself or before a trailing comment (described in original issue).

Fix

Improved the handling of removed empty statements by preserving following same-line comments, aligning blank-line behavior with rustfmt's standard vertical spacing, avoiding incorrect comment recovery on stripped semicolons.

In practice, it is consistent for the following three cases:

• if a line only contains a redundant ;, removes that line and lets normal newline handling apply
• if a line is ; <comment>, removes only the redundant ; and keeps the comment correctly indented on its own line
• surrounding blank lines respect the configured upper/lower bounds