Bug 246501

/WebKitGTK/TestWebKitAccessibility /webkit/WebKitAccessibility/accessible/children-changed

This exact failure is not always happening due to the SDK issue from bug246471, so I had to completely ignore fatal warnings to get to these.

EWS history shows this has been failing in a while (couldn't pick up where yet).

Notes from investigation:

  * The test creates a `div` with two `p` - `foo` and `bar` - which are the accessible objects. Working fine.
  * Then the test creates a new `p`, called `baz`, working fine.
  * Then the test removes `foo`, working fine.
  * Then the test changes the role - through JS - of `bar` and checks whether the existing object had its role changed without detach+attach
    * This test fails, with the existing object still having the role `paragraph`
    * If I get the children at the same position again, it already has the right `button` role
  * Also, in line: https://github.com/webkit/webkit/blob/main/Tools/TestWebKitAPI/Tests/WebKitGtk/TestWebKitAccessibility.cpp#L388
    * if we replace the `test->stopEventTimer(0, 0.5_s)` with an actual timer, two events are fired:
    * `object:children-changed:remove` with `detail1 == 1`
    * `object:children-changed:add` with `detail1 == 0`