Add StaticTextSlice kind to FormatElement enum (#2873)

Given our current parser abstractions, we need the ability to tell `ruff_formatter` to print a pre-defined slice from a fixed string of source code, which we've introduced here as `FormatElement::StaticTextSlice`.

crates/ruff_formatter/src/builders.rs

@@ -8,6 +8,7 @@ use std::borrow::Cow;
 use std::cell::Cell;
 use std::marker::PhantomData;
 use std::num::NonZeroU8;
+use std::rc::Rc;
 use Tag::*;
 
 /// A line break that only gets printed if the enclosing `Group` doesn't fit on a single line.
@@ -303,6 +304,34 @@ impl std::fmt::Debug for DynamicText<'_> {
     }
 }
 
+/// Creates a text from a dynamic string and a range of the input source
+pub fn static_text_slice(text: Rc<str>, range: TextRange) -> StaticTextSlice {
+    debug_assert_no_newlines(&text[range]);
+
+    StaticTextSlice { text, range }
+}
+
+#[derive(Eq, PartialEq)]
+pub struct StaticTextSlice {
+    text: Rc<str>,
+    range: TextRange,
+}
+
+impl<Context> Format<Context> for StaticTextSlice {
+    fn fmt(&self, f: &mut Formatter<Context>) -> FormatResult<()> {
+        f.write_element(FormatElement::StaticTextSlice {
+            text: self.text.clone(),
+            range: self.range,
+        })
+    }
+}
+
+impl std::fmt::Debug for StaticTextSlice {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        std::write!(f, "StaticTextSlice({})", &self.text[self.range])
+    }
+}
+
 /// String that is the same as in the input source text if `text` is [`Cow::Borrowed`] or
 /// some replaced content if `text` is [`Cow::Owned`].
 pub fn syntax_token_cow_slice<'a, L: Language>(