readSync and writeSync use dispatch_minimal now.

Note cli/dispatch_minimal.rs ops are not yet included in cli/ops.

This is part of work towards #2730

* Propagate Url::to_file_path() errors instead of panicking

Removes the magic number hack to switch between flatbuffers and the
minimal dispatcher.

Adds machinery to pass the op_id through the shared_queue.

And throws without allow-env 

This is a minor feature which complicates the build signifigantly.
Removing to ease refactoring the build system:
https://github.com/denoland/deno/issues/2608

* remove fetch_source_file_and_maybe_compile_async and 
  replace it with State.fetch_compiled_module

* remove SourceFile.js_source()

* introduce CompiledModule which is basically the same as
  deno::SourceInfo and represents arbitrary file that has been 
  compiled to JS module

* introduce //cli/compilers module containing all compilers

* introduce JsCompiler which is a no-op compiler
  - output is the same as input, no compilation takes place
  - it is used for MediaType::JavaScript and MediaType::Unknown

* introduce JsonCompiler that wraps JSON in default export

* support JS-to-JS compilation using checkJs

* merge SourceFileFetcher trait and FileFetcher struct

* move logic related to source file fetching to //cli/file_fetcher.rs

* use Result when creating new ThreadSafeState

* rename `ModuleMetaData` to `SourceFile` and remove TS specific
  functionality

* add `TsCompiler` struct encapsulating processing of TypeScript files

* move `SourceMapGetter` trait implementation to `//cli/compiler.rs`

* add low-level `DiskCache` API for general purpose caches and use it in
  `DenoDir` and `TsCompiler` for filesystem access

* don't use hash-like filenames for compiled modules, instead use
  metadata file for storing compilation hash

* add `SourceFileCache` for in-process caching of loaded files for fast
  subsequent access

* define `SourceFileFetcher` trait encapsulating loading of local and
  remote files and implement it for `DenoDir`

* define `use_cache` and `no_fetch` flags on `DenoDir` instead of using
  in fetch methods