[api] allow CSL receiver to gather parent CSL capabilities (#7991)

This commit extends the Thread API to allow a CSL Receiver application
to adjust its CSL parameters depending on the parent capabilities.

Specifically, it might decide to switch to polling operation instead
of CSL synchronization when the attached parent does not support CSL
Transmitter role (Thread Version 2) or it advertises poor CSL accuracy
or uncertainty.

include/openthread/instance.h

@@ -53,7 +53,7 @@ extern "C" {
  * @note This number versions both OpenThread platform and user APIs.
  *
  */
-#define OPENTHREAD_API_VERSION (231)
+#define OPENTHREAD_API_VERSION (232)
 
 /**
  * @addtogroup api-instance

include/openthread/thread.h

@@ -138,6 +138,14 @@ typedef struct
     uint8_t      mAge;                 ///< Time last heard
     bool         mAllocated : 1;       ///< Router ID allocated or not
     bool         mLinkEstablished : 1; ///< Link established with Router ID or not
+    uint8_t      mVersion;             ///< Thread version
+
+    /**
+     * Parent CSL parameters are only relevant when OPENTHREAD_CONFIG_MAC_CSL_RECEIVER_ENABLE is enabled.
+     *
+     */
+    uint8_t mCslClockAccuracy; ///< CSL clock accuracy, in ± ppm
+    uint8_t mCslUncertainty;   ///< CSL uncertainty, in ±10 us
 } otRouterInfo;
 
 /**