ART: Add entrypoint and intrinsic for Math.pow().

MathBenchmarks.java#timePow results on taimen's little cores
fixed at frequency 1401600 with forced JIT compilation:
  - before:
    - X32: 356.33 (@FastNative), 315.39 (@CriticalNative)
    - X64: 357.31 (@FastNative), 315.37 (@CriticalNative)
  - after (LICM defeats the benchmark):
    - X32: 2.88
    - X64: 2.87
  - after but with kAllSideEffects to prevent LICM:
    - X32: 275.42
    - X64: 275.67

Test: Rely on TreeHugger.
Bug: 70727450
Change-Id: Iaa31f70acabbd57c163cfeafe02eed67c1348861
diff --git a/runtime/intrinsics_list.h b/runtime/intrinsics_list.h
index d007728..da08793 100644
--- a/runtime/intrinsics_list.h
+++ b/runtime/intrinsics_list.h
@@ -136,6 +136,7 @@
   V(MathAsin, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "asin", "(D)D") \
   V(MathAtan, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "atan", "(D)D") \
   V(MathAtan2, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "atan2", "(DD)D") \
+  V(MathPow, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "pow", "(DD)D") \
   V(MathCbrt, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "cbrt", "(D)D") \
   V(MathCosh, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "cosh", "(D)D") \
   V(MathExp, kStatic, kNeedsEnvironmentOrCache, kNoSideEffects, kNoThrow, "Ljava/lang/Math;", "exp", "(D)D") \