cmake_command: Add command to INVOKE other commands by name

Fixes: #18392

Help/command/macro.rst

@@ -42,11 +42,15 @@ can be invoked through any of
   foo()
   Foo()
   FOO()
+  cmake_command(INVOKE foo)
 
 and so on. However, it is strongly recommended to stay with the
 case chosen in the macro definition.  Typically macros use
 all-lowercase names.
 
+The :command:`cmake_command(INVOKE ...)` command can also be used to invoke the
+macro.
+
 Arguments
 ^^^^^^^^^