Adds a new flag v8_deprecate_get_isolate that marks
HeapObject::GetIsolate/GetHeap, Handle<T>(T*) and handle<T>(T*) as
[[deprecated]]. Deprecation warnings are not converted to errors so an
entire build can be completed to collect all the warnings.

Also adds a new script tools/collect_deprecation_stats.sh which runs the
build (assuming the flag is set) and collects the number of uses of
deprecated functions. E.g. at the time of upload, we get:

Total deprecated calls: 2265
    515 GetHeap
    842 GetIsolate
    210 handle
    698 Handle

Bug: v8:7786
Change-Id: I7043c597fa90bc77759a357ef3c2a5fefe933491
Reviewed-on: https://chromium-review.googlesource.com/1082478Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53475}