sapi: Canonicalize @defgroup and @file comments

Adjust group identifier and names to be in line with a common pattern.
Use common phrases for the group and file brief descriptions.

Update #3706.

cpukit/sapi/src/getversionstring.c

@@ -1,9 +1,10 @@
 /**
  * @file
  *
- * @brief Get the RTEMS Version as a String
+ * @ingroup RTEMSImplClassic
  *
- * @ingroup ClassicRTEMS
+ * @brief This source file contains the implementation of
+ *   rtems_get_version_string().
  */
 
 /*