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

4 files changed, 31 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();
diff --git a/tests/038_checkjs.js.out b/tests/038_checkjs.js.out
new file mode 100644
index 000000000..deaf77211
--- /dev/null
+++ b/tests/038_checkjs.js.out
@@ -0,0 +1,15 @@
+[WILDCARD]
+error TS2552: Cannot find name 'consol'. Did you mean 'console'?
+
+[WILDCARD]tests/038_checkjs.js:2:1
+
+2 consol.log("hello world!");
+[WILDCARD]
+error TS2552: Cannot find name 'Foo'. Did you mean 'foo'?
+
+[WILDCARD]tests/038_checkjs.js:6:17
+
+6 const foo = new Foo();
+[WILDCARD]
+Found 2 errors.
+[WILDCARD]
\ No newline at end of file
diff --git a/tests/038_checkjs.test b/tests/038_checkjs.test
new file mode 100644
index 000000000..6385c9bb7
--- /dev/null
+++ b/tests/038_checkjs.test
@@ -0,0 +1,5 @@
+# checking if JS file is run through TS compiler
+args: run --reload --config tests/038_checkjs.tsconfig.json tests/038_checkjs.js
+check_stderr: true
+exit_code: 1
+output: tests/038_checkjs.js.out
diff --git a/tests/038_checkjs.tsconfig.json b/tests/038_checkjs.tsconfig.json
new file mode 100644
index 000000000..08ac60b6c
--- /dev/null
+++ b/tests/038_checkjs.tsconfig.json
@@ -0,0 +1,5 @@
+{
+  "compilerOptions": {
+    "checkJs": true
+  }
+}