Fixing a bug in determining tab to select in a split view

The compare function provided to max_element has the largest element as
the first parameter followed by the current element. So the logic needs
to be reversed. This kind of worked previously due to the fact that we
call SelectTab on both MousePressed and MouseReleased events. However,
there are two issues that still show up. First is clicking on a tab
while the split view is active would cause a tab switch (added a
regression test for this). Second, the tab with the focus would be
incorrect.

Bug: 408011094
Change-Id: I2acc4798a6ed6211e07ce4dc3b56bec387da7efb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6455992
Commit-Queue: Eshwar Stalin <estalin@chromium.org>
Reviewed-by: Alison Gale <agale@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1447162}