[clang-tools-extra] [clang-tools-extra][docs] Add documentation for clang-reorder-fields (PR #178446)

[via cfe-commits]

================
@@ -0,0 +1,423 @@
+====================
+Clang-Reorder-Fields
+====================
+
+.. contents::
+
+.. toctree::
+  :maxdepth: 1
+
+:program:`clang-reorder-fields` is a refactoring tool to reorder fields in
+C/C++ structs and classes. This tool automatically updates:
+
+- Field declarations in the record definition
+- Constructor initializer lists in C++ classes
+- Aggregate initialization expressions (both C and C++)
+- Designated initializer lists (C++20)
+
+This can be useful for optimizing memory layout, improving cache performance,
+or conforming to coding standards that require specific field orderings.
+
+Example usage
+-------------
+
+Basic struct reordering
+~~~~~~~~~~~~~~~~~~~~~~~~
----------------
EugeneZelenko wrote:

```suggestion
Basic struct reordering
~~~~~~~~~~~~~~~~~~~~~~~
```

https://github.com/llvm/llvm-project/pull/178446