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 
AnnotationStateModelType,
  AnnotationType,
  arrayByteLength,
  arraysToBytes,
  assert,
  BaseException,
  bytesToString,
  CMapCompressionType,
  createObjectURL,
  createPromiseCapability,
  createValidAbsoluteUrl,
  DocumentActionEventType,
  encodeToXmlString,
  escapeString,
  FONT_IDENTITY_MATRIX,
  FontType,
  FormatError,
  getModificationDate,
  getVerbosityLevel,
  IDENTITY_MATRIX,
  ImageKind,
  info,
  InvalidPDFException,
  isArrayBuffer,
  isArrayEqual,
  isAscii,
  isBool,
  IsEvalSupportedCached,
  IsLittleEndianCached,
  isNum,