Adds ModuleSpecifier, which wraps a URL. This is now passed around instead of
specifier and resolver strings.

It's unnecessary indirection and is preventing the ability to easily
pass isolate references into the dispatch and dyn_import closures.

Note: this changes how StartupData::Script is executed. It's no longer done
during Isolate::new() but rather lazily on first poll or execution.

This patch makes it so that RecursiveLoad doesn't own the Isolate, so
Worker::execute_mod_async does not consume itself.

Previously Worker implemented Loader, but now ThreadSafeState does.

This is necessary preparation work for dynamic import (#1789) and import
maps (#1921)

* Compiler no longer has its own Tokio runtime. Compiler handles one
  message and then exits.

* Uses the simpler ts.CompilerHost interface instead of
  ts.LanguageServiceHost.

* avoids recompiling the same module by introducing a hacky but simple
  `hashset<string>` that stores the module names that have been already
  compiled.

* Removes the CompilerConfig op.

* Removes a lot of the mocking stuff in compiler.ts like `this._ts`. It
  is not useful as we don't even have tests.

* Turns off checkJs because it causes fmt_test to die with OOM.

Op dispatch is now dynamically dispatched, so slightly less efficient.
The immeasurable perf hit is a reasonable trade for the API simplicity
that is gained here.

Changes "deno --types" to "deno types"
and "deno --prefetch" to "deno prefetch"

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.