bench: explicitly make all current benchmarks "high" priority

no-functional changes. Only have set the priority level explicitly
on every BENCHMARK macro call.

src/bench/examples.cpp

@@ -18,4 +18,4 @@ static void Trig(benchmark::Bench& bench)
     });
 }
 
-BENCHMARK(Trig);
+BENCHMARK(Trig, benchmark::PriorityLevel::HIGH);