UseSWIG: Do not use MAIN_DEPENDENCY on custom commands (#15480)

Add the dependency on the main swig input source file as a normal
DEPENDS option.  We cannot use MAIN_DEPENDENCY because if there are
multiple target languages then multiple custom commands would want to
use the same MAIN_DEPENDENCY, but at most one custom command may specify
a given source file as its MAIN_DEPENDENCY.  Exposed by a CMP0057
warning.

Modules/UseSWIG.cmake

@@ -204,8 +204,7 @@ macro(SWIG_ADD_SOURCE_TO_MODULE name outfiles infile)
     ${swig_include_dirs}
     -o "${swig_generated_file_fullname}"
     "${swig_source_file_fullname}"
-    MAIN_DEPENDENCY "${swig_source_file_fullname}"
-    DEPENDS ${SWIG_MODULE_${name}_EXTRA_DEPS}
+    DEPENDS "${swig_source_file_fullname}" ${SWIG_MODULE_${name}_EXTRA_DEPS}
     COMMENT "Swig source")
   set_source_files_properties("${swig_generated_file_fullname}" ${swig_extra_generated_files}
     PROPERTIES GENERATED 1)