Progressbar: Remove _value() and always sanitize value option

[Scott González]

There's no reason for the value option to ever be invalid. We should force it to a valid value on init and whenever max, or value changes. The validation on change needs to occur in _setOptions() so that we properly handle a call like .progressbar( "option", { value 120, max: 150 } ) which would try to set the value above the current max.

[k_borchers]

I started working on this but noticed a number of things that confuse me and before I create more tickets I am hoping to get some other input.

1 - The min is not configurable. It is 0 and can not be updated. I don't think that is right. 2 - ARIA min/max are not updated if the option is changed 3 - There is no API doc for the max (and missing min) option

[Scott González]

1) The lack of a min option is by design. When do you ever have negative progress?

2) That's a bug.

3) It's surprising that it's missing on the planning wiki too. I'll update the wiki and the API docs.

[Kris Borchers]

Progressbar: Refactor to better handle option changes and sanitize values. Fixes #8785 - Progressbar: Remove _value() and always sanitize value option

Changeset: 8976bc7e3d1f03254f914297b1be1b730690d2b8