Similar to JSCall, we can also replace uninitialized JSConstruct nodes
with SOFT deopts to ensure that we don't generate unnecessary dead code.
This for example shows up in the hot parts of the Node event emitter
currently where the generic code for handling events with 4 or more
parameters might not have been run, but we still generate most of the
code because the new Array call in the beginning is not turned into
a SOFT deopt immediately.

Drive-by-fix: Also refactor the BytecodeGraphBuilder's handling of
Construct bytecodes a bit to reduce the amount of code duplication.

BUG=v8:4551, v8:5267
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2958253002
Cr-Commit-Position: refs/heads/master@{#46339}