Fix the grid artifacts in simplex noise

Skew grid artifacts were shown due to the recent GPU driver update that
may have changed some floating point computation. Making the hash
function integer based to mitigate floating point precision issue.

Skewed grid can be only shown if the hash function produces different
gradient vectors in the same simplex vertex. Since the hash function
produces "discontinuous" random values, a small difference in the input
could cause a huge difference in the output. This is why it's more
robust to use integer based hash.

Bug: 315533269
Flag: NA
Test: Visually inspect
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:47ab14aa59ecdf013e5e87573a164114f8503d61)
Merged-In: I4bdc69a7dd8e6c3919a7c0594bebf37b83fd946a
Change-Id: I4bdc69a7dd8e6c3919a7c0594bebf37b83fd946a