Set "shader_param/" prefix in Shader::has_param()

(cherry picked from commit ffbb211bbe5d4c7cad881d9c34bccf0978226d1f)

scene/resources/shader.cpp

@@ -154,7 +154,7 @@ bool Shader::is_text_shader() const {
 
 bool Shader::has_param(const StringName &p_param) const {
 
-	return params_cache.has(p_param);
+	return params_cache.has("shader_param/" + p_param);
 }
 
 void Shader::_update_shader() const {