Use lowest-number error position for line/col position displayed for aggregate positions
Summary: For aggregate positions that are all part of the same file (some displayed with an intermediary ':' between them), the top-level line/col displayed next to the file name needs to reflect the lowest marker number across _all_ position groups for that file, not just the lowest marker for a specific position group.
Reviewed By: Wilfred
Differential Revision:
D22851908
fbshipit-source-id:
20c0be376dcff16ecd763a69e20df656360fbcce