Bug 1363508 - Part 1: Spoofing pen/touch pointer events into mouse pointer events when fingerprinting resistance is on r=arthuredelstein,masayuki,smaug

The pointerType field in the pointer event will reveal the details of
users' hardware; this is a fingerprinting vector. So, we would spoof all
types of pointer events into mouse type pointer events for protecting
users from browser fingerprinting when fingerprinting resistance is on.

In this patch, we would spoof the pointerType as well as other fields
that mouse pointer events don't support, like pressure, tiltX/Y and so
on when fingerprinting resistance is on.

Differential Revision: https://phabricator.services.mozilla.com/D6003

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extra : moz-landing-system : lando