Format comment before parameter default correctly (#7870)

**Summary** Handle comment before the default values of function
parameters correctly by inserting a line break instead of space after
the equals sign where required.

```python
def f(
    a = # parameter trailing comment; needs line break
    1,
    b =
    # default leading comment; needs line break
    2,
    c = ( # the default leading can only be end-of-line with parentheses; no line break
        3
    ),
    d = (
        # own line leading comment with parentheses; no line break
        4
    )
)
```

Fixes #7603

**Test Plan** Added the different cases and one more complex case as
fixtures.

crates/ruff_python_formatter/tests/snapshots/format@statement__function.py.snap

@@ -390,6 +390,32 @@ try:
     #comment
 except ImportError:
     pass
+
+# https://github.com/astral-sh/ruff/issues/7603
+def default_arg_comments(
+    a: str = #a
+    "a",
+    b: str =
+    #b
+    "b",
+    c: str =( #c
+        "c"
+    ),
+    d: str =(
+        #d
+        "d"
+    )
+):
+    print(a, b, c, d)
+
+def default_arg_comments2(#
+        x: int#=
+        = #
+        #
+        123#
+        #
+):
+    print(x)
 ```
 
 ## Output
@@ -940,6 +966,33 @@ try:
     # comment
 except ImportError:
     pass
+
+
+# https://github.com/astral-sh/ruff/issues/7603
+def default_arg_comments(
+    a: str =  # a
+    "a",
+    b: str =
+    # b
+    "b",
+    c: str = (  # c
+        "c"
+    ),
+    d: str = (
+        # d
+        "d"
+    ),
+):
+    print(a, b, c, d)
+
+
+def default_arg_comments2(  #
+    x: int =  # =  #
+    #
+    123,  #
+    #
+):
+    print(x)
 ```