focus a form widget onmouseup instead of onmousedown

[liucougar]

(In [13893]) fixes #6888: call focus synchronously onmouseup for form widget this should fix issues where a button onclick handler wants set focus on something else but in the end, the button still get the focus

[bill]

See #5434; above checkin implements different fix for that ticket.

[bill]

(In [21299]) Move onclick --> focus() code from _CssStateMixin back to _FormWidget.

This code was added in to _FormWidget in [11894] and [13893] so that clicking a non-focusable part of a form widget (ValidationTextBox validation icon, or the spinner up/down arrows) would cause the form widget to focus. But, it's inappropriate for bigger widgets, in particular Editor.

Actually I was nervous that it wouldn't even work correctly for ComboButton (which has two focus points), but it seems to.

Refs #5434, #6888, #10613. Fixes #10708 !strict.

[bill]

(In [21387]) Put onMouseUp --> focus() handling in FormWidget not FormValueWidget, as it was in the 1.4 release.

Otherwise on hrome clicking a button doesn't give it focus, which leads to problems restoring focus when closing a Dialog. (Dialog_menu.html is actually failing because focus is restored to the DateTextBox inside of the dialog, Refs #5434, #6888, #10613. Fixes #10708 !strict.