This patch clarifies that v8::Isolate is a single threaded creature,
which can only be accessed from other threads in special circumstances.
To ensure optimal operation in Deno, we remove v8::Locker, which ought
to be unnecessary when a thread is dedicated to each Isolate and the
Isolates never move between threads.
There are valid use-cases for v8::Locker, and we hope to address them in
future versions of rusty_v8.
Co-authored-by: Bert Belder <bertbelder@gmail.com>
