Fix more warnings and do some small optimizations (#1356)

* Fix more warnings and do some small optimizations

* Fix more warnings in ValueConversions

* Clean up some decompiler names and fix an unnecessary transformation around commands

* Use (way) more compact data structure for slot map

* Minor tweaks
Such as map directly in the collector

* I hate vanilla javac
Revert map changes in latest commit

src/main/java/carpet/script/argument/FileArgument.java

@@ -515,7 +515,7 @@ public class FileArgument
     {
         try (BufferedReader reader = Files.newBufferedReader(filePath, StandardCharsets.UTF_8))
         {
-            return new JsonParser().parse(new JsonReader(reader));
+            return JsonParser.parseReader(reader);
         }
         catch (JsonParseException e)
         {