AddFileDependencies: Deprecate this unnecessary module

Document that one can call `set_property` directly instead.

Help/manual/cmake-modules.7.rst

@@ -15,7 +15,6 @@ These modules are loaded using the :command:`include` command.
 .. toctree::
    :maxdepth: 1
 
-   /module/AddFileDependencies
    /module/AndroidTestUtilities
    /module/BundleUtilities
    /module/CheckCCompilerFlag
@@ -272,6 +271,7 @@ Deprecated Utility Modules
 .. toctree::
    :maxdepth: 1
 
+   /module/AddFileDependencies
    /module/CMakeDetermineVSServicePack
    /module/CMakeExpandImportedTargets
    /module/CMakeForceCompiler

Help/release/dev/AddFileDependencies-deprecate.rst

+AddFileDependencies-deprecate
+-----------------------------
+
+* The :module:`AddFileDependencies` module is deprecated.
+  Port projects to use :command:`set_property` directly.

Modules/AddFileDependencies.cmake

@@ -5,13 +5,25 @@
 AddFileDependencies
 -------------------
 
+.. deprecated:: 3.20
+
 Add dependencies to a source file.
 
 .. code-block:: cmake
 
-  add_file_dependencies(<source> <files>)
+  add_file_dependencies(<source> <files>...)
 
 Adds the given ``<files>`` to the dependencies of file ``<source>``.
+
+Do not use this command in new code.  It is just a wrapper around:
+
+.. code-block:: cmake
+
+  set_property(SOURCE <source> APPEND PROPERTY OBJECT_DEPENDS <files>...)
+
+Instead use the :command:`set_property` command to append to the
+:prop_sf:`OBJECT_DEPENDS` source file property directly.
+
 #]=======================================================================]
 
 function(add_file_dependencies _file)