Introduce AutoindentMode parameter to Buffer::edit

This controls whether or not we preserve the relative indentation
of inserted text blocks.

Co-authored-by: Mikayla Maki <mikayla.c.maki@gmail.com>

crates/editor/src/display_map/block_map.rs

@@ -1164,7 +1164,7 @@ mod tests {
 
         // Insert a line break, separating two block decorations into separate lines.
         let buffer_snapshot = buffer.update(cx, |buffer, cx| {
-            buffer.edit([(Point::new(1, 1)..Point::new(1, 1), "!!!\n")], cx);
+            buffer.edit([(Point::new(1, 1)..Point::new(1, 1), "!!!\n")], None, cx);
             buffer.snapshot(cx)
         });