Do not consider f-strings with escaped newlines as multiline (#14624)

## Summary

This PR fixes a bug in the f-string formatting to not consider the
escaped newlines for `is_multiline`. This is done by checking if the
f-string is triple-quoted or not similar to normal string literals.

This is not required to be gated behind preview because the logic change
for `is_multiline` was added in
https://github.com/astral-sh/ruff/pull/14454.

## Test Plan

Add a test case which formats differently on `main`:
https://play.ruff.rs/ea3c55c2-f0fe-474e-b6b8-e3365e0ede5e

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

@@ -424,3 +424,10 @@ xxxxxxxxxxxxxxxx = f"aaaaaaaaaaaaaaaaaaaaa {
     expression } bbbbbbbbbbbbbbbbbbbbbbbb" + (
     yyyyyyyyyyyyyy + zzzzzzzzzzz
 )
+
+# This is not a multiline f-string, but the expression is too long so it should be
+# wrapped in parentheses.
+f"hellooooooooooooooooooooooo \
+        worlddddddddddddddddddddddddddddddddd" + (aaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbb)
+aaaaaaaaaaa = f"hellooooooooooooooooooooooo \
+        worlddddddddddddddddddddddddddddddddd" + (aaaaaaaaaaaaaaaaaaaaaaaaaa + bbbbbbbbbbbbbbbbbbb)

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

@@ -326,3 +326,24 @@ assert False, +"Implicit concatenated string" "uses {} layout on {} format".form
 "a" f'{1=: "abcd \'\'}'
 f'{1=: "abcd \'\'}' "a"
 f'{1=: "abcd \'\'}' f"{1=: 'abcd \"\"}"
+
+# These strings contains escaped newline characters and should be joined, they are
+# not multiline strings.
+f"aaaaaaaaaaaaaaaa \
+        bbbbbbbbbbb" "cccccccccccccc \
+               ddddddddddddddddddd"
+b"aaaaaaaaaaaaaaaa \
+        bbbbbbbbbbb" b"cccccccccccccc \
+               ddddddddddddddddddd"
+f"aaaaaaaaaaaaaaaa \
+        bbbbbbbbbbb" "cccccccccccccc \
+               ddddddddddddddddddd"  # comment 1
+(f"aaaaaaaaaaaaaaaa \
+        bbbbbbbbbbb" "cccccccccccccc \
+               ddddddddddddddddddd")  # comment 2
+(
+    f"aaaaaaaaaaaaaaaa \
+            bbbbbbbbbbb" # comment 3
+    "cccccccccccccc \
+            ddddddddddddddddddd"  # comment 4
+)