Parse triple quoted string annotations as if parenthesized (#15387)

## Summary

Resolves #9467 

Parse quoted annotations as if the string content is inside parenthesis.
With this logic `x` and `y` in this example are equal:

```python
y: """
   int |
   str
"""

z: """(
    int |
    str
)
"""
```

Also this rule only applies to triple
quotes([link](https://github.com/python/typing-council/issues/9#issuecomment-1890808610)).

This PR is based on the
[comments](https://github.com/astral-sh/ruff/issues/9467#issuecomment-2579180991)
on the issue.

I did one extra change, since we don't want any indentation tokens I am
setting the `State::Other` as the initial state of the Lexer.

Remaining work:

- [x] Add a test case for red-knot.
- [x] Add more tests.

## Test Plan

Added a test which previously failed because quoted annotation contained
indentation.
Added an mdtest for red-knot.
Updated previous test.

Co-authored-by: Dhruv Manilawala <dhruvmanila@gmail.com>
Co-authored-by: Micha Reiser <micha@reiser.io>

crates/ruff_python_parser/src/lib.rs

@@ -72,7 +72,9 @@ pub use crate::token::{Token, TokenKind};
 
 use crate::parser::Parser;
 
-use ruff_python_ast::{Expr, Mod, ModExpression, ModModule, PySourceType, Suite};
+use ruff_python_ast::{
+    Expr, Mod, ModExpression, ModModule, PySourceType, StringFlags, StringLiteral, Suite,
+};
 use ruff_python_trivia::CommentRanges;
 use ruff_text_size::{Ranged, TextRange, TextSize};
 
@@ -166,6 +168,65 @@ pub fn parse_expression_range(
         .into_result()
 }
 
+/// Parses a Python expression as if it is parenthesized.
+///
+/// It behaves similarly to [`parse_expression_range`] but allows what would be valid within parenthesis
+///
+/// # Example
+///
+/// Parsing an expression that would be valid within parenthesis:
+///
+/// ```
+/// use ruff_python_parser::parse_parenthesized_expression_range;
+/// # use ruff_text_size::{TextRange, TextSize};
+///
+/// let parsed = parse_parenthesized_expression_range("'''\n int | str'''", TextRange::new(TextSize::new(3), TextSize::new(14)));
+/// assert!(parsed.is_ok());
+pub fn parse_parenthesized_expression_range(
+    source: &str,
+    range: TextRange,
+) -> Result<Parsed<ModExpression>, ParseError> {
+    let source = &source[..range.end().to_usize()];
+    let parsed =
+        Parser::new_starts_at(source, Mode::ParenthesizedExpression, range.start()).parse();
+    parsed.try_into_expression().unwrap().into_result()
+}
+
+/// Parses a Python expression from a string annotation.
+///
+/// # Example
+///
+/// Parsing a string annotation:
+///
+/// ```
+/// use ruff_python_parser::parse_string_annotation;
+/// use ruff_python_ast::{StringLiteral, StringLiteralFlags};
+/// use ruff_text_size::{TextRange, TextSize};
+///
+/// let string = StringLiteral {
+///     value: "'''\n int | str'''".to_string().into_boxed_str(),
+///     flags: StringLiteralFlags::default(),
+///     range: TextRange::new(TextSize::new(0), TextSize::new(16)),
+/// };
+/// let parsed = parse_string_annotation("'''\n int | str'''", &string);
+/// assert!(!parsed.is_ok());
+/// ```
+pub fn parse_string_annotation(
+    source: &str,
+    string: &StringLiteral,
+) -> Result<Parsed<ModExpression>, ParseError> {
+    let range = string
+        .range()
+        .add_start(string.flags.opener_len())
+        .sub_end(string.flags.closer_len());
+    let source = &source[..range.end().to_usize()];
+    if string.flags.is_triple_quoted() {
+        parse_parenthesized_expression_range(source, range)
+    } else {
+        parse_expression_range(source, range)
+    }
+}
+
 /// Parse the given Python source code using the specified [`Mode`].
 ///
 /// This function is the most general function to parse Python code. Based on the [`Mode`] supplied,
@@ -582,6 +643,11 @@ pub enum Mode {
     /// The code consists of a single expression.
     Expression,
 
+    /// The code consists of a single expression and is parsed as if it is parenthesized. The parentheses themselves aren't required.
+    /// This allows for having valid multiline expression without the need of parentheses
+    /// and is specifically useful for parsing string annotations.
+    ParenthesizedExpression,
+
     /// The code consists of a sequence of statements which can include the
     /// escape commands that are part of IPython syntax.
     ///