Avoid multiline expression if format specifier is present (#11123)

## Summary

This PR fixes the bug where the formatter would format an f-string and
could potentially change the AST.

For a triple-quoted f-string, the element can't be formatted into
multiline if it has a format specifier because otherwise the newline
would be treated as part of the format specifier.

Given the following f-string:
```python
f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
    variable:.3f} ddddddddddddddd eeeeeeee"""
```

The formatter sees that the f-string is already multiline so it assumes
that it can contain line breaks i.e., broken into multiple lines. But,
in this specific case we can't format it as:

```python
f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
    variable:.3f
} ddddddddddddddd eeeeeeee"""
```
                     
Because the format specifier string would become ".3f\n", which is not
the original string (`.3f`).

If the original source code already contained a newline, they'll be
preserved. For example:
```python
f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
    variable:.3f
} ddddddddddddddd eeeeeeee"""
```

The above will be formatted as:
```py
f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {variable:.3f
} ddddddddddddddd eeeeeeee"""
```

Note that the newline after `.3f` is part of the format specifier which
needs to be preserved.
The Python version is irrelevant in this case.

fixes: #10040 

## Test Plan

Add some test cases to verify this behavior.

crates/ruff_python_formatter/resources/test/fixtures/ruff/expression/fstring.py

@@ -129,6 +129,10 @@ x = f"{  # comment 12
     {'x': 1, 'y': 2} }"
 x = f"{    # comment 13
     {'x': 1, 'y': 2} = }"
+# But, if there's a format specifier or a conversion flag then we don't need to add
+# any whitespace at the end
+x = f"aaaaa { {'aaaaaa', 'bbbbbbb', 'ccccccccc'}!s} bbbbbb"
+x = f"aaaaa { {'aaaaaa', 'bbbbbbb', 'ccccccccc'}:.3f} bbbbbb"
 
 # But, in this case, we would split the expression itself because it exceeds the line
 # length limit so we need not add the extra space.
@@ -207,6 +211,29 @@ f"{ # comment 15
 }"  # comment 19
 # comment 20
 
+# Single-quoted f-strings with a format specificer can be multiline
+f"aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
+    variable:.3f} ddddddddddddddd eeeeeeee"
+
+# But, if it's triple-quoted then we can't or the format specificer will have a
+# trailing newline
+f"""aaaaaaaaaaaaaaaa bbbbbbbbbbbbbbbbbb ccccccccccc {
+    variable:.3f} ddddddddddddddd eeeeeeee"""
+
+# But, we can break the ones which don't have a format specifier
+f"""fooooooooooooooooooo barrrrrrrrrrrrrrrrrrr {
+        xxxxxxxxxxxxxxx:.3f} aaaaaaaaaaaaaaaaa { xxxxxxxxxxxxxxxxxxxx } bbbbbbbbbbbb"""
+
+# Throw in a random comment in it but surpise, this is not a comment but just a text
+# which is part of the format specifier
+aaaaaaaaaaa = f"""asaaaaaaaaaaaaaaaa {
+        aaaaaaaaaaaa + bbbbbbbbbbbb + ccccccccccccccc + dddddddd:.3f
+     # comment
+} cccccccccc"""
+aaaaaaaaaaa = f"""asaaaaaaaaaaaaaaaa {
+        aaaaaaaaaaaa + bbbbbbbbbbbb + ccccccccccccccc + dddddddd:.3f
+     # comment} cccccccccc"""
+
 # Conversion flags
 #
 # This is not a valid Python code because of the additional whitespace between the `!`