[clang] [clang-format][CMake] Generate formatting options docs during build (PR #113739)

[Owen Pan via cfe-commits]

================
@@ -185,6651 +179,10 @@ the configuration (without a prefix: ``Auto``).
     subdirectories. This is also possible through the command line, e.g.:
     ``--style={BasedOnStyle: InheritParentConfig, ColumnLimit: 20}``
 
+.. This section of the file is automatically generated by the
+  dump_format_style.py tool and should be updated manually.
 .. START_FORMAT_STYLE_OPTIONS
----------------
owenca wrote:

```suggestion
.. START_FORMAT_STYLE_OPTIONS

..
  This section is automatically generated by the dump_format_style.py script and
  should not be updated manually.
```

https://github.com/llvm/llvm-project/pull/113739