Standalone language server (#885)

Free the language server from Kiama and implement a test suite.
Found some bugs while reimplementing, and I've confirmed all of them
also exist in the old server.
It should be on-par with the old implementation in terms of features and
bugs.

Depends on effekt-lang/kiama#9.

**Differences to the old Server:**

* Added unit test suite
* New server runs single threaded and sequentially
* Compile on `didChange`, by default
* No Monto anymore, added a custom `$/effekt/publishIR` notification
instead.

**Implementation status:**

* [x] `initialize`
* [x] `shutdown` - not covered by unit tests - they cannot handle the
process exit
* [x] `exit` - not covered by unit tests - they cannot handle the
process exit
* [x] setTrace
* [x] Diagnostics `afterCompilation`
* [x] `didChange`
* [x] `didOpen`
* [x] `didSave`
* [x] `didClose`
* [ ] `hover`
  * [x] for symbols
* [ ] 🐛 for holes: #549
* [ ] `documentSymbol`
  * [x] impl & test
* [ ] 🐛 Fix spurious symbols at `(0, 0)`:
#895
* [ ] `references`
  * [x] impl & test
* [ ] 🐛 Fix not all references being returned (see test case):
#896
* [x] `inlayHint`
  * [x] impl & test
* [x] 🐛 inlayHints and hoverInfo sometimes return null (as in old
implementation):
* [x] inlayHints: #876
(fixed in #894)
* [x] hoverInfo: #366
(**can't reproduce**)
Note that the timing issue should be gone as we now run on
`newSingleThreadExecutor` (which claims "Tasks are guaranteed to execute
sequentially"), the caching issues have been fixed in #894.
* [ ] `getCodeActions`
  * [x] port impl from old server
* [ ] 🐛 impl doesn't even work in old server:
#897
* [x] `definition`
* [ ] `notebookDocument/*`
  * not implemented, student works on another branch
* [ ] publish IR (`$/effekt/publishIR`), replacing Monto
  * [x] impl server and test (this PR)
* [x] impl client (effekt-lang/effekt-vscode#63)
* [ ] 🐛 many options (e.g. `target`) don't work because the server
only runs the compiler frontend - same issue with old server


Important questions to reviewers:

* [x] `effekt/jvm/src/main/scala/effekt/KiamaUtils.scala` is
MPL-licensed code from Kiama - what do we do with this?
  * I decided to move it to Kiama to be safe.

---------

Co-authored-by: Marvin Borner <[email protected]>

Author: timsueberkrueb

effekt/jvm/src/main/scala/effekt/Main.scala

@@ -17,14 +17,19 @@ object Main {
       parseArgs(args)
     } catch {
       case e: ScallopException =>
-        System.err.println(e.getMessage())
+        System.err.println(e.getMessage)
         return
     }
 
     if (config.server()) {
-      Server.launch(config)
+      val serverConfig = ServerConfig(
+        debug = config.debug(),
+        debugPort = config.debugPort()
+      )
+      val server = new Server(config)
+      server.launch(serverConfig)
     } else if (config.repl()) {
-      new Repl(Server).run(config)
+      new Repl(new Driver {}).run(config)
     } else {
       compileFiles(config)
     }
@@ -43,8 +48,9 @@ object Main {
    * Compile files specified in the configuration.
    */
   private def compileFiles(config: EffektConfig): Unit = {
+    val driver = new Driver {}
     for (filename <- config.filenames()) {
-      Server.compileFile(filename, config)
+      driver.compileFile(filename, config)
     }
   }
 }