Unstable formatting of parenthesized implicit string concatenation

[konstin]

This snippet causes unstable formatting:

x = ("""aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa""" """bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb""")

We first break it, then realize it fits in a line without the parentheses and undo that:

---
--- Formatted once
+++ Formatted twice
@@ -1,4 +1 @@
-x = (
-    """aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"""
-    """bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"""
-)
+x = """aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa""" """bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"""
---

Formatted once:
---
x = (
    """aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"""
    """bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"""
)
---

Formatted twice:
---
x = """aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa""" """bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"""
---

[MichaReiser]

This could be related to it being in the assignment position.

Playground

[MichaReiser]

I'm taking this on as it seems to be fixed in my local branch for #6271