refactor: cleanup compiler pipeline (#2686)

* 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

1 files changed, 6 insertions, 0 deletions

diff --git a/tests/038_checkjs.js b/tests/038_checkjs.js
new file mode 100644
index 000000000..628d3e376
--- /dev/null
+++ b/tests/038_checkjs.js
@@ -0,0 +1,6 @@
+// console.log intentionally misspelled to trigger a type error
+consol.log("hello world!");
+
+// the following error should be ignored and not output to the console
+// eslint-disable-next-line
+const foo = new Foo();