Fix regression on IE10 clicking blank screen to close drop down.

Squash of two commits:

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Fix regression on IE10 clicking blank screen to close drop down.

An e.preventDefault() call on MSPointerDown prevents the button from getting focus,
so I stopped doing it for that case.  This is a minimal fix.  Other approaches include:

  1. remove the e.preventDefault() call for all cases
  2. make focus manager listen for touch/mouse events in the capture phase rather than the
bubbling phase, to avoid missing the event due to a stopPropagation() call; it used
to do this except for IE6-8, but I normalized the behavior in 9965406.

Fixes #17262.  Refs #13048, #13341.
(cherry picked from commit 76216d6d829f011a87ccd11ee12d3a862d6e2e88)

(cherry picked from commit d5eef52f83e77b9d501ce0309b4f4d69b64c6a04)

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Support unprefixed pointer events
(change applies to _HasDropDown only)

Refs #17600

(cherry picked from commit 275211f84351d18b000b35cb495e8efc6fde7937)

Conflicts:
	form/TextBox.js

(cherry picked from commit b9dd78e03fa2d3542350f767e46d2771654b6517)

Conflicts:
	_CssStateMixin.js
	form/TextBox.js
	tests/_HasDropDown.html
	tests/_Widget-on.html
	tests/tree/Tree_ObjectStoreModel.html