Fix formatter non-convergence with EOL comment before else if

[kbrunham-intel]

Summary

Fixes #2540: formatter non-convergence when an EOL comment sits between end and a following else if.

When end carried a trailing EOL comment, PushEndIntoElsePartition merged that end+comment into the else-if header partition. fit-else-expand then treated the header as wider than the eventual printed line, so the first format kept the else-if assignment on one line and the second wrap split it — format(format(x)) != format(x).

Change: skip merging end into the else partition when the end leaf contains an EOL comment (else must start on the next line anyway when preceded by a comment).

Test plan

• Added FormatterEndToEndTest.EndElseIfWithEOLCommentConverges covering comment-on-own-line and comment-already-on-end
• bazel test //verible/verilog/formatting:formatter_test
• CI green on this PR

[linux-foundation-easycla]

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• ✅ login: kbrunham-intel / name: Kalen Brunham (af81883)

[hzeller]

Thanks for your contribution - Sorry for the delay in the review, I was a bit busy the last couple of weeks.

Looks good. Can you rebase, as there were other changes in the formatter_test that now require a merge ?