Rework testMemoryGrowPreservesDataMemOp tests so that they only test the
first and last 5 offsets within the page, instead of every offset.

Slight logic change: instead of storing the value C - offset (where C is
a constant that is different for 32 and 16 memops), we store just the
value offset. This allows us to combine the logic for all 3 memops (32,
16, and 8). But we need to add a modulo so that in the 8 bit case, we
don't store a value that exceeds the maximum (the other cases will never
hit a case that exceeds the max).

Bug: v8:7783
Change-Id: Ibfdc77555ba2ca26391eba303050a03538f6012d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2117633Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66879}