[clang] [clang-format] Support BraceWrapping.AfterNamespace with AllowShortNamespacesOnASingleLine (PR #123010)

[Owen Pan via cfe-commits]

================
@@ -660,17 +672,18 @@ class LineJoiner {
 
       assert(Limit >= L1.Last->TotalLength + 3);
       const auto InnerLimit = Limit - L1.Last->TotalLength - 3;
-      const auto MergedLines = tryMergeNamespace(I + 1, E, InnerLimit);
+      const auto MergedLines =
+          tryMergeNamespace(BraceOpenLine + 1, E, InnerLimit, OpenBraceWrapped);
       if (MergedLines == 0)
         return 0;
-      const auto N = MergedLines + 2;
+      const auto N = MergedLines + 2 + OpeningBraceLineOffset;
----------------
owenca wrote:

```suggestion
      const auto N = MergedLines + LinesToBeMerged;
```

https://github.com/llvm/llvm-project/pull/123010