For interpreted functions, use the optimized code slot in the feedback
vector to store an optimization marker (optimize/in optimization queue)
rather than changing the JSFunction's code object. Then, adapt the
self-healing mechanism to also dispatch based on this optimization
marker. Similarly, replace SFI marking with optimization marker checks
in CompileLazy.

This allows JSFunctions to share optimization information (replacing
shared function marking) without leaking this information across native
contexts. Non I+TF functions (asm.js or --no-turbo) use a
CheckOptimizationMarker shim which generalises the old
CompileOptimized/InOptimizationQueue builtins and also checks the same
optimization marker as CompileLazy and InterpreterEntryTrampoline.

This is a reland of https://chromium-review.googlesource.com/c/509716

Change-Id: I02b790544596562373da4c9c9f6afde5fb3bcffe
Reviewed-on: https://chromium-review.googlesource.com/535460Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45997}