op_fetch_module_meta_data is an op that is used by the TypeScript
compiler. TypeScript requires this op to be sync. However the
implementation of the op does things on the event loop (like fetching
HTTP resources).

In certain situations this can lead to deadlocks. The runtime's thread
pool can be filled with ops waiting on the result of
op_fetch_module_meta_data. The runtime has a maximum number of
threads it can use (the number of logical CPUs on the system).

This patch changes tokio_util::block_on to launch a new Tokio runtime
for evaluating the future, thus bipassing the max-thread problem.

This is only an issue in op_fetch_module_meta_data. Other synchronous
ops are truly synchornous, not interacting with the event loop.  TODO
comments are added to direct future development.

Crashes while running wrk against
js/deps/https/deno.land/std/http/http_bench.ts

This reverts commit 972ac038.

This is to work around Tokio's panic recovery feature.
Ref https://github.com/tokio-rs/tokio/issues/495
Ref https://github.com/tokio-rs/tokio/issues/209
Ref https://github.com/denoland/deno/issues/1311
Fixes #2097

To better distinguish the deno_core crate from the executable deno,
which will now be called "the cli" internally.

This disables a few tests which are broken still:
- tests/error_004_missing_module.test
- tests/error_005_missing_dynamic_import.test
- tests/error_006_import_ext_failure.test
- repl_test test_set_timeout
- repl_test test_async_op
- repl_test test_set_timeout_interlaced
- all of permission_prompt_test

This is in preperation for core integration.

Adds deno.listen(), deno.dial(), deno.Listener and deno.Conn.

By using the tokio default runtime.

This patch makes all of the ops thread safe.

Adds libdeno to JS globals to make for easier testing.

Preliminary work for #733.