Optimize add/set/delete operations for string keys in Maps and Sets

This was previously landed in commit 8599f5f, but failed the
collections mjsunit test on ia32 with --deopt-every-n=1. The fixed
patch adds a ClearFlag(HValue::kCanOverflow) call after every
arithmetic operation, which should remove all the deopt points in these
intrinsics.

Ideally, it seems like there should be a way to verify that there are
no deopt points for these inline optimized functions, since there's
nothing to deopt to. But I don't currently know of such a thing.

Review URL: https://codereview.chromium.org/782073002

Cr-Commit-Position: refs/heads/master@{#25715}