TextBox: add robot test for selectOnClick feature

[bill]

Should be testing:

1. Click once, click again - the first time a TextBox is clicked all the text is selected, and the second time it's clicked should get a plain caret (aka empty selection). Need to make sure that the second click doesn't reselect all the text.

2. Tab into TextBox, then click it - the click should not reselect all the text, same principle as above.

3 Tab into TextBox, out of TextBox, shift-back in, then click it - this is to make sure that the event handler (which fires on focus) get cleared on blur

4. Mouse-down, mouse-move to select some text, mouse-up - it should just select the text that the user indicated, not select all the text. IE, a user specifically selecting some text should cancel the selectOnClick feature.

[Douglas Hays]

(In [21032]) Fixes #10448. Add automated tests for selectOnClick function.

[Douglas Hays]

(In [21033]) Refs #10448. Tweak automated tests for selectOnClick function.