How do computer science admissions committees process GRE essays sent with the scores?
I am surprised, but this does appear to be true.  From the ets website we have the following:


  ETS also makes available test-taker photos and essay responses on the Analytical Writing section of the GRE® revised General Test to designated score recipients as part of an institutional portal. Photos and Analytical Writing essay responses of all individuals who report their scores to institutions on or after July 1, 2014, are included in the portal. The photo and essay responses from each GRE revised General Test administration you select from your five-year reportable history will be made available in the portal as part of your score record to the institutions you designated to receive your scores on or after July 1, 2014.


(In some sense, I'm even more surprised they are making photos of test-takers available.)  As for how the admissions committee processes these essays, others on the site can speak more directly to this, particularly in computer science.  However, I'm certain this will vary from department to department (assuming any department looks at them at all).  I suspect the admissions committee of many departments will not even be aware these essays are available through the ETS institutional portal.  Of those that are aware these exist, I would be surprised if much weight were placed on these.  These will convey almost no incremental information to an admissions committee.  (I suppose if you scored a 0 and the rest of your application was outstanding, and the committee knew these were available, someone might look to see what happened.  Maybe.)