Re-factor the BaseException.name handling, and clean-up some code

Once we're finally able to get rid of SystemJS, which is unfortunately still blocked on [bug 1247687](https://bugzilla.mozilla.org/show_bug.cgi?id=1247687), we might also want to clean-up (or even completely remove) the `BaseException` abstraction and simply extend `Error` directly instead.

At that point we'd need to (explicitly) set the `name` on each class anyway, so this patch is essentially preparing for future clean-up. Furthermore, after the `BaseException` abstraction was added there's been *multiple* issues filed about third-party minification breaking our code since `this.constructor.name` is not guaranteed to always do what you intended.

While hard-coding the strings indeed feels quite unfortunate, it's likely the "best" solution to avoid the problem described above.

src/core/jpx.js

@@ -19,7 +19,7 @@ import { ArithmeticDecoder } from "./arithmetic_decoder.js";
 
 class JpxError extends BaseException {
   constructor(msg) {
-    super(`JPX error: ${msg}`);
+    super(`JPX error: ${msg}`, "JpxError");
   }
 }