Updating metadata for 1.6.2
Updating source version to 1.6.3-pre
Do not fire watchers when setting existing NaN value to NaN

Fixes #17513.
(cherry picked from commit 531b8f46acc8acba87d55a0338649bfc30ae58c9)

Conflicts:
	_WidgetBase.js
	tests/_Widget-attr.html