LibSQL+SQLServer+SQLStudio+sql: Use proper types for SQL IPC and IDs

When storing IDs and sending values over IPC, this changes SQLServer to:

1. Stop using -1 as a nominal "bad" ID. Store the IDs as unsigned, and
   use Optional in the one place that the IPC needs to indicate an ID
   was not allocated.

2. Let LibIPC encode/decode enumerations (SQLErrorCode) on our behalf.

3. Use size_t for array sizes.

Userland/DevTools/SQLStudio/MainWidget.h

@@ -65,7 +65,7 @@ private:
     Optional<DeprecatedString> read_next_line_of_editor();
     size_t m_current_line_for_parsing { 0 };
     int m_editor_line_level { 0 };
-    int m_connection_id { 0 };
+    u64 m_connection_id { 0 };
 };
 
 }