feat(extmarks): add "undo_restore" flag to opt out of undo-restoring

It is a design goal of extmarks that they allow precise tracking
of changes across undo/redo, including restore the exact positions
after a do/undo or undo/redo cycle. However this behavior is not useful
for all usecases. Many plugins won't keep marks around for long after
text changes, but uses them more like a cache until some external source
(like LSP semantic highlights) has fully updated to changed text and
then will explicitly readjust/replace extmarks as needed.

Add a "undo_restore" flag which is true by default (matches existing
behavior) but can be set to false to opt-out of this behavior.

Delete dead u_extmark_set() code.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/nvim/api/keysets.h b/src/nvim/api/keysets.h
index 18f6d5368b..d435262ff3 100644
--- a/src/nvim/api/keysets.h
+++ b/src/nvim/api/keysets.h
@@ -48,6 +48,7 @@ typedef struct {
   String conceal;
   Boolean spell;
   Boolean ui_watched;
+  Boolean undo_restore;
 } Dict(set_extmark);
 
 typedef struct {