TOOLS: add test script for property change notifications

TOOLS/lua/observe-all.lua

@@ -0,0 +1,16 @@
+-- Test script for property change notification mechanism.
+
+function format_property_val(v)
+    if type(v) == "table" then
+        return mp.format_table(v) -- undocumented function; might be removed
+    else
+        return tostring(v)
+    end
+end
+
+for i,name in ipairs(mp.get_property_native("property-list")) do
+    mp.observe_property(name, "native", function(name, val)
+        print("property '" .. name .. "' changed to '" ..
+              format_property_val(val) .. "'")
+    end)
+end