Fix IDE formatting of correctly formatted files with trailing newlines

[mszabo-wikia]

Since D60978552, we special-case removing a range of lines during IDE formatting so that T188437747 does not rear its ugly head. However, when document-formatting a file that is already correctly formatted save for some spurious trailing newlines, this logic ends up consuming the last non-newline line. So, only shift the start offset if the last changed line wasn't a trailing line that got removed.

Add a test and wire up hh_single_ide_format with the OSS dune build so that IDE format tests can be run.

[meta-codesync[bot]]

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