[php] Generate PHP type declarations

We now automatically generate PHP type declarations for PHP >= 8.0.

The generated code still compiles with PHP 7.x but without type declarations.

Examples/test-suite/li_factory.i

@@ -16,7 +16,8 @@
   struct Geometry {
     enum GeomType{
       POINT,
-      CIRCLE
+      CIRCLE,
+      SHAPELESS
     };
 
     virtual ~Geometry() {}

Examples/test-suite/php/argout_runme.php

@@ -20,11 +20,14 @@ $tr=copy_intp(4);
 check::equal(4,inctr($tr),"4==incr($tr)");
 check::equal(5,intp_value($tr),"5==$tr");
 
-# Check the voidhandle call, first with null
+# Check the voidhandle call, first with NULL and then with the SWIG\p_void we
+# get from the first call.
 $handle=NULL;
-voidhandle($handle);
-check::equal(get_class($handle),"SWIG\\_p_void",'$handle is not _p_void');
-$handledata=handle($handle);
-check::equal($handledata,"Here it is","\$handledata != \"Here it is\"");
+for ($i=0; $i != 1; $i++) {
+  voidhandle($handle);
+  check::equal(get_class($handle),"SWIG\\_p_void",'$handle is not _p_void');
+  $handledata=handle($handle);
+  check::equal($handledata,"Here it is","\$handledata != \"Here it is\"");
+}
 
 check::done();

Examples/test-suite/php/li_factory_runme.php

@@ -17,4 +17,7 @@ $point = Geometry::create(Geometry::POINT);
 $w = $point->width();
 check::equal($w, 1.0, "w failed");
 
+$point = Geometry::create(Geometry::SHAPELESS);
+check::equal($point, NULL, "NULL failed");
+
 check::done();