[clang] [clang-format] Add `AllowShortNamespacesOnASingleLine` option (PR #105597)

[Owen Pan via cfe-commits]

================
@@ -4484,7 +4484,7 @@ TEST_F(FormatTest, FormatsCompactNamespaces) {
                "} // namespace A",
                Style);
 
-  Style.ColumnLimit = 40;
+  Style.ColumnLimit = 41;
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owenca wrote:

```suggestion
  Style.ColumnLimit = 40;
```
See below.

https://github.com/llvm/llvm-project/pull/105597