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

[Owen Pan via cfe-commits]

================
@@ -688,8 +701,8 @@ class LineJoiner {
     if (L2.First->isNot(tok::r_brace) || L2.First->MustBreakBefore)
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owenca wrote:

```suggestion
    if (L2.First->isNot(TT_NamespaceRBrace) || L2.First->MustBreakBefore)
```

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