Options disable feature added

[Viijay-Kr]

Reasons for making this change

Selection widget option elements currently does not have the ability to disable an option/options through schema.I had to deal with a use case in my project where I needed to disable some parent option elements so that they become non selectable.I went through the code and I found that a extra attribute must be added.

So this PR introduces a feature to disable a StringField.UiWidget options through schema

{ "type":"string", "enum":["foo","bar"], "enumNames":["Foo","Bar"], "enumDisabled":["bar"] }

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
  • If I'm adding a new section, I've updated the Table of Content
• I'm adding or updating code
  • I've added and/or updated tests
  • I've updated docs if needed
  • I've run npm run cs-format on my branch to conform my code to prettier coding style
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

[glasserc]

Hi, thanks for your contribution! I'm not crazy about the use of enumDisabled in the schema. enumNames are already nonstandard (see #532), and disabling of an option seems like something that belongs in the uiSchema.

Also, can you add tests when you add a feature like this? Thanks!

[glasserc]

This PR was superseded by #708.