Enable clippy::single_char_pattern (#8727)

This PR enables the
[`clippy::single_char_pattern`](https://rust-lang.github.io/rust-clippy/master/index.html#/single_char_pattern)
rule and fixes the outstanding violations.

Release Notes:

- N/A

crates/vim/src/command.rs

@@ -41,7 +41,7 @@ pub fn command_interceptor(mut query: &str, cx: &AppContext) -> Option<CommandIn
     //
     // For now, you can only do a replace on the % range, and you can
     // only use a specific line number range to "go to line"
-    while query.starts_with(":") {
+    while query.starts_with(':') {
         query = &query[1..];
     }
 
@@ -321,16 +321,16 @@ pub fn command_interceptor(mut query: &str, cx: &AppContext) -> Option<CommandIn
         "0" => ("0", StartOfDocument.boxed_clone()),
 
         _ => {
-            if query.starts_with("/") || query.starts_with("?") {
+            if query.starts_with('/') || query.starts_with('?') {
                 (
                     query,
                     FindCommand {
                         query: query[1..].to_string(),
-                        backwards: query.starts_with("?"),
+                        backwards: query.starts_with('?'),
                     }
                     .boxed_clone(),
                 )
-            } else if query.starts_with("%") {
+            } else if query.starts_with('%') {
                 (
                     query,
                     ReplaceCommand {

crates/vim/src/normal/paste.rs

@@ -135,8 +135,8 @@ fn paste(_: &mut Workspace, action: &Paste, cx: &mut ViewContext<Workspace>) {
                         } else {
                             (clipboard_text.to_string(), first_selection_indent_column)
                         };
-                    let line_mode = to_insert.ends_with("\n");
-                    let is_multiline = to_insert.contains("\n");
+                    let line_mode = to_insert.ends_with('\n');
+                    let is_multiline = to_insert.contains('\n');
 
                     if line_mode && !before {
                         if selection.is_empty() {
@@ -480,7 +480,7 @@ mod test {
                 the_
                 ˇfox jumps over
                 _dog"}
-            .replace("_", " "), // Hack for trailing whitespace
+            .replace('_', " "), // Hack for trailing whitespace
         )
         .await;
         cx.assert_shared_clipboard("lazy").await;

crates/vim/src/test/neovim_backed_test_context.rs

@@ -72,7 +72,7 @@ impl NeovimBackedTestContext {
         let test_name = thread
             .name()
             .expect("thread is not named")
-            .split(":")
+            .split(':')
             .last()
             .unwrap()
             .to_string();
@@ -122,7 +122,7 @@ impl NeovimBackedTestContext {
     }
 
     pub async fn set_shared_state(&mut self, marked_text: &str) {
-        let mode = if marked_text.contains("»") {
+        let mode = if marked_text.contains('»') {
             Mode::Visual
         } else {
             Mode::Normal
@@ -188,7 +188,7 @@ impl NeovimBackedTestContext {
 
     pub async fn assert_shared_state(&mut self, marked_text: &str) {
         self.is_dirty = false;
-        let marked_text = marked_text.replace("•", " ");
+        let marked_text = marked_text.replace('•', " ");
         let neovim = self.neovim_state().await;
         let neovim_mode = self.neovim_mode().await;
         let editor = self.editor_state();

crates/vim/src/test/neovim_connection.rs

@@ -392,7 +392,7 @@ impl NeovimConnection {
                 // the content of the selection via the "a register to get the shape correctly.
                 self.nvim.input("\"aygv").await.unwrap();
                 let content = self.nvim.command_output("echo getreg('a')").await.unwrap();
-                let lines = content.split("\n").collect::<Vec<_>>();
+                let lines = content.split('\n').collect::<Vec<_>>();
                 let top = cmp::min(selection_row, cursor_row);
                 let left = cmp::min(selection_col, cursor_col);
                 for row in top..=cmp::max(selection_row, cursor_row) {