Add keywords for dealing with stale elements

[Brownies]

For my use case it would be nice to have some keywords to be able to deal with elements that get removed from the DOM. Something along the lines of

• Wait Until Element Is Stale
• Get Element Staleness
• Element Should (Not) Be Stale

I wrote a rudimentary Python plugin at work using Selenium's staleness_of condition. I got the OK to use the plugin as a base and spend some time so I'd be willing to try and provide a PR as well if this feature makes sense and would be a good fit for the library.

[emanlove]

I know personally I have been hesitant to add an exhaustive set of keywords which specifically wait until some state. I was just now talking with Tatu about a question someone raised about waiting. He showed me this solution

element = WebDriverWait(self.driver, 30, ignored_exceptions=(StaleElementReferenceException,)).until(
                EC.element_to_be_clickable((By.ID, "description"))
            )

I was thinking a generic Wait until Element State Is/Is Not might be the solution. There is an full list of expected conditions that we could take advantage of .. I was just going to put in a reminder ticket for myself and saw your request. Do you think this (with a Get Element State and Element State Should (Not) Be keywords) fulfill your request?

[Brownies]

Yeah that would be great!