Use numeric comparator when sorting mimetype indices in MimeTypeDisplayOrder.prioritize (#316826)

Use numeric comparator when sorting mimetype indices

MimeTypeDisplayOrder.prioritize sorted numeric indices with the default Array.prototype.sort, which compares values as strings. Once the display order grows to ~10+ mimetypes, indices like [2, 10] sort to [10, 2] so the reverse-iteration splice loop removes the wrong rows and the final order corrupts (duplicate / missing mimetypes). Pass an ascending numeric comparator. Adds a regression test with 12 mimetypes.