Adds a ForInPrepare Runtime function which returns a triple of
cache_type, cache_array and cache_length.

This requires adding support to CEntryStub to call runtime functions
which return a ObjectTriple - a struct containing three Object*
pointers. Also did some cleanup of the x64 CEntryStub to avoid
replicated code.

Replaces the interpreter's use of the ad-hock InterpreterForInPrepare
Runtime function with ForInPrepare in preparation for fixing deopt in
BytecodeGraphBuilder for ForIn (which will be done in a followup CL).

MIPS port contributed by Balazs Kilvady <balazs.kilvady@imgtec.com>.

BUG=v8:4280
LOG=N

Review URL: https://codereview.chromium.org/1576093004

Cr-Commit-Position: refs/heads/master@{#33334}