Fix various issues in libpkl (#1805)

* Fix possible SIGSEGV from host process.
   - Require that the same `pkl_exec_t` be used in the same OS thread; returning meaningful error if this fails
* Remove `System.exitProcess(1)` logic in NativeTransport; this would kill the host process too and isn't an appropriate action for a received ProtocolException
* Allow multiple calls to pkl_init without pkl_close; this limitation doesn't really make any sense
* Prefer calling methods defined in graal_isolate.h, instead of creating the same method via CEntryPoint
* Add a CMakeLists.txt so that CLion can follow the code and provide proper diagnostics
* Improve doc comments; describe params as either in or out

pkl-server/src/main/kotlin/org/pkl/server/Server.kt

@@ -231,7 +231,9 @@ class Server(private val transport: MessageTransport) : AutoCloseable {
         build()
       }
     } catch (e: IllegalArgumentException) {
-      throw ProtocolException(e.message ?: "Failed to create an evalutor. $e", e)
+      throw ProtocolException(e.message ?: "Failed to create an evaluator. $e", e)
+    } catch (e: IllegalStateException) {
+      throw ProtocolException(e.message ?: "Failed to create an evaluator. $e", e)
     }
   }