[keyserver] Go back to using window function for getMessageInfos

Summary:
The window function is a much more modern and civilized approach to this query.

I first introduced this in D4675, but then reverted it in D4796 because it caused ENG-957.

However, once I found that the window function approach solved ENG-2009, I spent a second thinking about how to change the window function to avoid the issue from ENG-957. The easy solution is just to move the LEFT JOIN uploads line to the outer query.

In addition, I noticed the window function also needed an ORDER BY, as it was exhibiting the same out-of-order weirdness that caused ENG-2009. Although it wasn't affecting the partition function, our JS code for parsing the results expects that they appear in a specific order.

Test Plan:
I tried to test this thoroughly given previous experiences.

• I manually composed a query that reproduces the current issue (ENG-2009)
• I edited it for the window function approach and saw that the issue was resolved
• I manually composed a query that reproduces the old issue (ENG-957)
• I edited it for the window function approach and saw that the old issue did not reappear
• I patched my production keyserver live after midnight ET to confirm that the missing content now appears
• I also live-tested to make sure the old issue was resolved by checking a chat that recently had a message with three images

Reviewers: tomek, atul

Reviewed By: tomek

Subscribers: abosh

Differential Revision: https://phab.comm.dev/D5349