This introduces a JSConvertReceiver operator to model the implicit
conversion of receiver values for sloppy callees. It is used by the
JSInliner for now, but can also be used to model direction function
calls that bypass call stubs.

Also note that a hint is passed to said operator whenever the source
structure constrains the receiver value type. This hint allows for
optimizations in the lowering of the operator.

The underlying specification in ES6, section 9.2.1.2 is the basis for
this implementation.

R=bmeurer@chromium.org
TEST=mjsunit/compiler/receiver-conversion
BUG=v8:4493, v8:4470
LOG=n

Review URL: https://codereview.chromium.org/1412223015

Cr-Commit-Position: refs/heads/master@{#31598}