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 
constructor(data) {
    this.change = data.change || "";
    this.changeEx = data.changeEx || null;
    this.commitKey = data.commitKey || 0;
    this.fieldFull = data.fieldFull || false;
    this.keyDown = data.keyDown || false;
    this.modifier = data.modifier || false;
    this.name = data.name;
    this.rc = true;
    this.richChange = data.richChange || [];
    this.richChangeEx = data.richChangeEx || [];
    this.richValue = data.richValue || [];
    this.selEnd = data.selEnd || -1;
    this.selStart = data.selStart || -1;
    this.shift = data.shift || false;
    this.source = data.source || null;
    this.target = data.target || null;
    this.targetName = "";
    this.type = "Field";
    this.value = data.value || "";
    this.willCommit = data.willCommit || false;
  }
}
class EventDispatcher {