Cherry-picked Fix redo after noop format (#34898)
Closes#31917
Previously, as of #28457 we used a hack, creating an empty transaction
in the history that we then merged formatting changes into in order to
correctly identify concurrent edits to the buffer while formatting was
happening. This caused issues with noop formatting however, as using the
normal API of the buffer history (in an albeit weird way) resulted in
the redo stack being cleared, regardless of whether the formatting
transaction included edits or not, which is the correct behavior in all
other contexts.
This PR fixes the redo issue by codifying the behavior formatting wants,
that being the ability to push an empty transaction to the history with
no other side-effects (i.e. clearing the redo stack) to detect
concurrent edits, with the tradeoff being that it must then manually
remove the transaction later if no changes occurred from the formatting.
The redo stack is still cleared when there are formatting edits, as the
individual format steps use the normal `{start,end}_transaction` methods
which clear the redo stack if the finished transaction isn't empty.
Release Notes:
- Fixed an issue where redo would not work after buffer formatting
(including formatting on save) when the formatting did not result in any
changes
Co-authored-by: Ben Kunkle <ben@zed.dev>
780db4ce76