With this change, we use Float64Pow for both Smi and Float inputs, also
introduce new speculative operator.

For this PoC
==========================================================
let result = [NaN]; // Avoid HeapNumber-boxing the results.

function slow(){
  for(let i = 0; i < 100000000; i++) {
    result[0] = i ** 2;
  }
}

start = Date.now();
slow();
console.log(Date.now() - start);
==========================================================
Before: 1313
After: 112

Bug: v8:11731
Change-Id: I07a1bde068bef8184b9f556be9d1fe2d6a288705
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2960064
Commit-Queue: Z Nguyen-Huu <duongn@microsoft.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75590}