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 
RICHTEXT: 0x2000000,
  RADIOSINUNISON: 0x2000000,
  COMMITONSELCHANGE: 0x4000000,
};
const AnnotationBorderStyleType = {
  SOLID: 1,
  DASHED: 2,
  BEVELED: 3,
  INSET: 4,
  UNDERLINE: 5,
};
const AnnotationActionEventType = {
  E: "MouseEnter",
  X: "MouseExit",
  D: "MouseDown",
  U: "MouseUp",
  Fo: "Focus",
  Bl: "Blur",
  PO: "PageOpen",
  PC: "PageClose",
  PV: "PageVisible",
  PI: "PageInvisible",
  K: "Keystroke",
  F: "Format",
  V: "Validate",
  C: "Calculate",
};
const DocumentActionEventType = {
  WC: "WillClose",
  WS: "WillSave",