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

And rename IsolateState to ThreadSafeState.

Also make ThreadSafeState directly implement Dispatch. This is simpler.

Reduces generics.

* Moves how snapshots are supplied to the Isolate. Previously they were
  given by Behavior::startup_data() but it was only called once at
  startup. It makes more sense (and simplifies Behavior) to pass it to the
  constructor of Isolate.
* Adds new libdeno type deno_snapshot instead of overloading
  deno_buf.
* Adds new libdeno method to delete snapshot deno_snapshot_delete().
* Renames deno_get_snapshot() to deno_snapshot_new().
* Makes StartupData hold references to snapshots. This was implicit when
  it previously held a deno_buf but is made explicit now. Note that
  include_bytes!() returns a &'static [u8] and we want to avoid
  copying that.

And model worker resources as Stream

Fixes #1742
Fixes #2021

* Refactored the way worker polling is scheduled and errors are handled.
* Share the worker future as a Shared

test case from @afinch7

This simplifies the Behavior trait and makes it more explicit where the
resolve callback is being made.

Also s/StartupScript/Script

* get_source_code_async
* fetch_module_meta_data_async
* fetch_module_meta_data_and_maybe_compile_async

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

Re-enables arm64 CI test

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.

Refactored permissions to be assignable on a per-isolate 
basis, and added a fix for #1858 to op_fetch_module_meta_data.

src/js_errors.rs takes care of source maps and color while
core/js_errors.rs is just the basic struct.

A new low-level crate with focus on speed. 
This doesn't yet hook into the existing code base.

Move module stuff into its own file.

Co-authored-by: NGreg Altman <g.s.altman@gmail.com>

and deno_respond

Allows for future asynchronous module loading.

Add support for import.meta.url

Fixes #1496