vim fixes for find&replace (#2995)

* allow replacing with the empty string to delete
* fix <enter> for ReplaceNext (in vim mode)

Release Notes:

- allow replacement to be empty

crates/project/src/search.rs

@@ -159,7 +159,7 @@ impl SearchQuery {
             )
         }
     }
-    pub fn with_replacement(mut self, new_replacement: Option<String>) -> Self {
+    pub fn with_replacement(mut self, new_replacement: String) -> Self {
         match self {
             Self::Text {
                 ref mut replacement,
@@ -169,7 +169,7 @@ impl SearchQuery {
                 ref mut replacement,
                 ..
             } => {
-                *replacement = new_replacement;
+                *replacement = Some(new_replacement);
                 self
             }
         }