[clang-tools-extra] [doc] Add documentation for clang-change-namespace (PR #148277)

[Eric Li via cfe-commits]

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@@ -0,0 +1,155 @@
+======================
+Clang-Change-Namespace
+======================
+
+.. contents::
+
+.. toctree::
+  :maxdepth: 1
+
+:program:`clang-change-namespace` can be used to change the surrounding
+namespaces of class/function definitions.
+
+Classes/functions in the moved namespace will have new namespaces while
+references to symbols (e.g. types, functions) which are not defined in the
+changed namespace will be correctly qualified by prepending namespace specifiers
+before them. This will try to add shortest namespace specifiers possible.
+
+When a symbol reference needs to be fully-qualified, this adds a `::` prefix to
+the namespace specifiers unless the new namespace is the global namespace. For
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tJener wrote:

Perhaps not a question on the documentation, but rather the tool. Why is the global namespace special in this regard? It seems like there could be name ambiguities that arise with moving to the global namespace.

https://github.com/llvm/llvm-project/pull/148277