[lldb][Format] Update std::deque formatter to account for libc++ naming changes

Cherry-picked the LLDB parts from:
```
commit c7df106
Author: Peng Liu <[email protected]>
Date:   Wed Nov 13 05:08:08 2024 -0500

    Unify naming of internal pointer members in std::vector and
std::__split_buffer (llvm#115517)
```

Addresses llvm#144555

Author: Michael137

lldb/examples/synthetic/libcxx.py

@@ -764,9 +764,10 @@ def update(self):
                     map_.GetChildMemberWithName("__end_cap_")
                 )
             else:
-                map_endcap = map_.GetChildMemberWithName(
-                    "__end_cap_"
-                ).GetValueAsUnsigned(0)
+                map_endcap = map_.GetChildMemberWithName("__cap_")
+                if not map_endcap.IsValid():
+                    map_endcap = map_.GetChildMemberWithName("__end_cap_")
+                map_endcap = map_endcap.GetValueAsUnsigned(0)
 
             # check consistency
             if not map_first <= map_begin <= map_end <= map_endcap: