MDL-44720 modinfo: make it easier to use cm_info instead of get_coursemodule_from_id

by adding function cm_info::get_course_module_record()

lib/datalib.php

@@ -1293,6 +1293,10 @@ function get_course_mods($courseid) {
 /**
  * Given an id of a course module, finds the coursemodule description
  *
+ * Please note that this function performs 1-2 DB queries. When possible use cached
+ * course modinfo. For example get_fast_modinfo($courseorid)->get_cm($cmid)
+ * See also {@link cm_info::get_course_module_record()}
+ *
  * @global object
  * @param string $modulename name of module type, eg. resource, assignment,... (optional, slower and less safe if not specified)
  * @param int $cmid course module id (id in course_modules table)
@@ -1347,6 +1351,10 @@ function get_coursemodule_from_id($modulename, $cmid, $courseid=0, $sectionnum=f
 /**
  * Given an instance number of a module, finds the coursemodule description
  *
+ * Please note that this function performs DB query. When possible use cached course
+ * modinfo. For example get_fast_modinfo($courseorid)->instances[$modulename][$instance]
+ * See also {@link cm_info::get_course_module_record()}
+ *
  * @global object
  * @param string $modulename name of module type, eg. resource, assignment,...
  * @param int $instance module instance number (id in resource, assignment etc. table)