[turbofan] Improve AstGraphBuilder::BuildToBoolean() for heap constants.
[turbofan] Improve AstGraphBuilder::BuildToBoolean() for heap constants.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/852963004

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#26082}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh