Fix indent for merge_imports

Example
---
```rust
mod tests {
    use foo$0::bar;
    use foo::baz;
    fn feature() {}
}
```

**Before this PR**

```rust
mod tests {
    use foo::{bar, baz};
        fn feature() {}
}
```

**After this PR**

```rust
mod tests {
    use foo::{bar, baz};
    fn feature() {}
}
```

Author: A4-Tacks

crates/ide-assists/src/handlers/merge_imports.rs

@@ -106,12 +106,21 @@ trait Merge: AstNode + Clone {
     ) -> Option<Vec<Edit>> {
         let mut edits = Vec::new();
         let mut merged = self.clone();
+        let mut replace = self;
+        let mut update_replace = |item: Self| {
+            if item.syntax().text_range().start() < replace.syntax().text_range().start() {
+                std::mem::replace(&mut replace, item)
+            } else {
+                item
+            }
+        };
+
         for item in items {
             merged = merged.try_merge(&item, cfg)?;
-            edits.push(Edit::Remove(item.into_either()));
+            edits.push(Edit::Remove(update_replace(item).into_either()));
         }
         if !edits.is_empty() {
-            edits.push(Edit::replace(self, merged));
+            edits.push(Edit::replace(replace, merged));
             Some(edits)
         } else {
             None
@@ -563,6 +572,62 @@ use foo::{bar, baz};
         );
     }
 
+    #[test]
+    fn mod_indent_whitespace() {
+        check_assist(
+            merge_imports,
+            r"
+mod tests {
+    use foo$0::bar;
+    use foo::baz;
+    fn feature() {}
+}
+",
+            r"
+mod tests {
+    use foo::{bar, baz};
+    fn feature() {}
+}
+",
+        );
+        check_assist(
+            merge_imports,
+            r"
+mod tests {
+    use foo$0::bar;
+    use foo::baz;
+
+    fn feature() {}
+}
+",
+            r"
+mod tests {
+    use foo::{bar, baz};
+
+    fn feature() {}
+}
+",
+        );
+        check_assist(
+            merge_imports,
+            r"
+mod tests {
+    use foo::bar;
+    use foo$0::baz;
+
+    fn feature() {}
+}
+",
+            r"
+mod tests {
+    use foo::{bar, baz};
+
+    fn feature() {}
+}
+",
+        );
+    }
+
     #[test]
     fn works_with_trailing_comma() {
         check_assist(

crates/syntax/src/syntax_editor/edits.rs

@@ -214,18 +214,18 @@ impl Removable for ast::Use {
     fn remove(&self, editor: &mut SyntaxEditor) {
         let make = SyntaxFactory::without_mappings();
 
-        let next_ws = self
+        let prev_ws = self
             .syntax()
-            .next_sibling_or_token()
+            .prev_sibling_or_token()
             .and_then(|it| it.into_token())
             .and_then(ast::Whitespace::cast);
-        if let Some(next_ws) = next_ws {
-            let ws_text = next_ws.syntax().text();
-            if let Some(rest) = ws_text.strip_prefix('\n') {
+        if let Some(prev_ws) = prev_ws {
+            let ws_text = prev_ws.syntax().text();
+            if let Some(rest) = ws_text.trim_end_matches(' ').strip_suffix('\n') {
                 if rest.is_empty() {
-                    editor.delete(next_ws.syntax());
+                    editor.delete(prev_ws.syntax());
                 } else {
-                    editor.replace(next_ws.syntax(), make.whitespace(rest));
+                    editor.replace(prev_ws.syntax(), make.whitespace(rest));
                 }
             }
         }