In the following spots a "MouseUp" eventName is being used, which does look inconsistent considering that the "Mouse Down"/"Mouse Enter"/"Mouse Exit" eventNames all have a space in them.
Is this inconsistency actually expected, or is it a simple typo? If the former, then a comment explaining *why* would be appropriate; otherwise we should just fix this :-)

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L806

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L945

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1034

 - https://github.com/mozilla/pdf.js/blob/25b84ce84c95ba06d1ee57e578672048269c39c1/src/display/annotation_layer.js#L1168

/cc @calixteman 
return Object.assign(Object.create(null), Object.fromEntries(iterable));
}
function isLittleEndian() {
  const buffer8 = new Uint8Array(4);
  buffer8[0] = 1;
  const view32 = new Uint32Array(buffer8.buffer, 0, 1);
  return view32[0] === 1;
}
const IsLittleEndianCached = {
  get value() {
    return shadow(this, "value", isLittleEndian());
  },
};
function isEvalSupported() {
  try {
    new Function(""); 
    return true;
  } catch (e) {
    return false;
  }
}
const IsEvalSupportedCached = {
  get value() {
    return shadow(this, "value", isEvalSupported());
  },
};
const hexNumbers = [...Array(256).keys()].map(n =>
  n.toString(16).padStart(2, "0")
);
class Util {