Add flag contradictions for "assert-types" flag and a README file for how
to add trials from the source side. Also restore "assert-types" and its
contradictions' probability since we can avoid contradictions now.

Bug: v8:1340816,v8:1336577
No-Try: true
Change-Id: I2a3af2d13cd2f9f542bec5c013c50bf26ff93cc1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3787878
Commit-Queue: Almothana Athamneh <almuthanna@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82133}