* @param {Map} fileOwners mapping of platform name to a list of files involved in the change located in that platform
 * @param {[FileMetadata]} fileMetadatas - gitStream's list of metadata about file changes in the PR including path
 * @returns {[Object]} Returns a list of objects for each platform containing info about the changes to files in that platform

 * @param {[FileMetadata]} fileMetadatas - gitStream's list of metadata about file changes in the PR including path
 * @returns {[Object]} Returns list of computed summary statistic objects for each platform in the input groupedFiles
 * @example {{ fileOwners | categorize(branch.diff.files_metadata) | changeStatistics(branch.diff.files_metadata) }}
 */
function computeStatistics(groupedFiles, fileMetadatas) {