fix: postfix completions include nots prefix-expr

Example
---
Like `is_foo`, `.not`, `.if`

```rust
fn main() {
    let is_foo = true;
    !is_foo.$0
}
```

**Before this PR**

```rust
fn main() {
    let is_foo = true;
    !if is_foo {
        $0
    }
}
```

**After this PR**

```rust
fn main() {
    let is_foo = true;
    if !is_foo {
        $0
    }
}
```

Author: A4-Tacks

crates/ide-completion/src/completions/postfix.rs

@@ -402,23 +402,28 @@ fn receiver_accessor(receiver: &ast::Expr) -> ast::Expr {
         .unwrap_or_else(|| receiver.clone())
 }
 
-/// Given an `initial_element`, tries to expand it to include deref(s), and then references.
+/// Given an `initial_element`, tries to expand it to include deref(s), not(s), and then references.
 /// Returns the expanded expressions, and the added prefix as a string
 ///
 /// For example, if called with the `42` in `&&mut *42`, would return `(&&mut *42, "&&mut *")`.
 fn include_references(initial_element: &ast::Expr) -> (ast::Expr, String) {
     let mut resulting_element = initial_element.clone();
     let mut prefix = String::new();
 
-    while let Some(parent_deref_element) =
-        resulting_element.syntax().parent().and_then(ast::PrefixExpr::cast)
-        && parent_deref_element.op_kind() == Some(ast::UnaryOp::Deref)
+    while let Some(parent) = resulting_element.syntax().parent().and_then(ast::PrefixExpr::cast)
+        && parent.op_kind() == Some(ast::UnaryOp::Deref)
     {
-        resulting_element = ast::Expr::from(parent_deref_element);
-
+        resulting_element = ast::Expr::from(parent);
         prefix.insert(0, '*');
     }
 
+    while let Some(parent) = resulting_element.syntax().parent().and_then(ast::PrefixExpr::cast)
+        && parent.op_kind() == Some(ast::UnaryOp::Not)
+    {
+        resulting_element = ast::Expr::from(parent);
+        prefix.insert(0, '!');
+    }
+
     while let Some(parent_ref_element) =
         resulting_element.syntax().parent().and_then(ast::RefExpr::cast)
     {
@@ -1121,6 +1126,27 @@ fn main() {
         )
     }
 
+    #[test]
+    fn postfix_completion_for_nots() {
+        check_edit(
+            "if",
+            r#"
+fn main() {
+    let is_foo = true;
+    !is_foo.$0
+}
+"#,
+            r#"
+fn main() {
+    let is_foo = true;
+    if !is_foo {
+    $0
+}
+}
+"#,
+        )
+    }
+
     #[test]
     fn postfix_completion_for_unsafe() {
         postfix_completion_for_block("unsafe");