Transform LdaNull/LdaUndefined followed by StrictEquality to TestNull/TestUndefined.
This would avoid a call to the compare IC. In the bytecode-graph builder these are
mapped to StrictEqual javascript operator. When reducing this operator, we already
optimize the cases for null/undefined.

BUG=v8:4280

Review-Url: https://codereview.chromium.org/2554723004
Cr-Commit-Position: refs/heads/master@{#41768}