[cla][patch] Form.validate() will indicate errors in the form

[nathan]

Make Form.validate() turn all the invalid or required-but-blank fields yellow, and focus on the first invalid (or required-but-blank) field. It is a way to visually expose to the user that things aren't quite right.

Implementation notes: widget.isValid() won't be removed. widget.validate is extended to return the valid state (a boolean). Form.validate is a new method that calls widget.validate for each field - and in the event that one of them is invalid, it focuses on the first invalid.

[doughays]

Needs further discussion...

[nathan]

Patch which adds: 1 - dijit.form.Form.validate(), 2 - returns the boolean state from ValidationTextBox?.validate (and all subclasses), 3 - adds a testcase

[nathan]

Update to formValidationPatch - which contains a test case.

[nathan]

Updated patch - fixes scrolling tooltip issue and moves test case into Form.html

[doughays]

(In [12731]) Fixes #6005. Proxy commit for nathan. Added Form.validate() method that focuses the first invalid widget found. Changed widget.validate() method to return isValid boolean.