deps: upgrade v8 to 3.19.0
v8: reapply floating patches
stream_wrap: MayContainNonAscii() is deprecated

V8 3.19.0 deprecates v8::String::MayContainNonAscii(). It always returns
true so there is not much point in keeping the call site around.
test: fix up weakref.cc after v8 api change
test: fix up weakref.cc deprecation warnings
util: make util.log handle non strings like console.log

util.log will fail on input that does not support .toString(). Have it
use console.log() instead. Includes tests for hairy data types.

Fixes #5349.