Don't use the touch rect when targetting above the touch handles

Don't use the touch rect when targetting above the touch handles

The touch selection handles are positioned below the selected line of
text. Currently, we use the touch radius to make targetting the handles
easier, but this can make it difficult for the user to interact with the
selected line of text, e.g., to reposition the cursor by tapping.

Fix this by not preventing the handles from consuming touches that are
strictly above the touch handle region.

BUG=522250

Review URL: https://codereview.chromium.org/1294933006

Cr-Commit-Position: refs/heads/master@{#344374}