state=Stable does not check for visibility

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**Describe the bug**
I have recently seen that state=stable does not check visible the same way that state=visible does. I have created a simple test with directly using browser library. The keyword with state=stable passes, while the keyword with state=visible fails.
In the library it states that "| ``stable`` | to be both ``visible`` and ``stable``. |"

`browser.Wait For Elements State    selector=//xpath[.="text"]    state=stablebrowser.

Wait For Elements State    selector=//xpath[.="text"]    state=visible`

**To Reproduce**
Steps to reproduce the behavior:
1. setup a test like above in the description
2. Check a simple xpath that is always visible
3. Run the test and put a debug on the first keyword
4. Change the HTML code in the CSS to display: none or add "hidden" to the HTML element.
5. Continue the test run
6. Observe that the state=stable passes
7. Observe that the state=visible fails

**Expected behavior**
I expect that the stated description of the code for the state=stable works as expected. But it does not check for visibility.
| ``stable`` | to be both ``visible`` and ``stable``. |

Start at the Browser library's `Wait For Elements State` keyword and reproduce the reported difference between `state=stable` and `state=visible` using an element changed to `display: none` or `hidden`. Done means `stable` follows the documented visibility behavior, with coverage confirming the hidden-element case.

Written by the indexing model from the issue text.