Fix RT priority docs (NFC) (#3098)

The ranges and which value was specified as highest were incorrect on
some of them. On Linux, the range is 1 to 99 with 99 being highest.

From `man 7 sched`:
```
Processes scheduled under one of the real-time policies (SCHED_FIFO,
SCHED_RR) have a sched_priority value in the range 1 (low) to 99 (high).
```

Also clean up the relevant javadoc and doxygen comments.

wpiutil/src/test/native/cpp/priority_mutex_test.cpp

@@ -55,7 +55,7 @@ void SetProcessorAffinity(int32_t core_id) {
 
 void SetThreadRealtimePriorityOrDie(int32_t priority) {
   struct sched_param param;
-  // Set realtime priority for this thread
+  // Set real-time priority for this thread
   param.sched_priority = priority + sched_get_priority_min(SCHED_RR);
   ASSERT_EQ(pthread_setschedparam(pthread_self(), SCHED_RR, &param), 0)
       << ": Failed to set scheduler priority.";