Fix ComposePanel focus traversal on windows with nvda (Windows)

[m-sasha]

ComposePanel keeps its own _isFocusable and _isRequestFocusEnabled flags, and doesn't call the superclass' methods on setFocusable and setRequestFocusEnabled. Unfortunately Swing is not a well-behaved object-oriented library, and calling the superclass' methods has side effects which are needed.

Component.setFocusable sets an isFocusTraversableOverridden flag which is consulted when determining the "next" focusable component (see DefaultFocusTraversalPolicy.accept()). This flag's value is, by default, FOCUS_TRAVERSABLE_UNKNOWN, causing isFocusTraversableOverridden() to return true, which causes the ComposePanel to be accepted by DefaultFocusTraversalPolicy.accept().

When NVDA is turned on, however, the accessibility system calls ComposePanel.isFocusTraversable, which sets this flag to FOCUS_TRAVERSABLE_DEFAULT, causing isFocusTraversableOverridden() to return false, which causes DefaultFocusTraversalPolicy.accept() to reject the ComposePanel. If Component.setFocusable has been called before that, this doesn't happen because the flag is set with:

        if (isFocusTraversableOverridden == FOCUS_TRAVERSABLE_UNKNOWN) {
            isFocusTraversableOverridden = FOCUS_TRAVERSABLE_DEFAULT;
        }

An alternative solution here would be for ComposePanel to override isFocusTraversable in addition to isFocusable, thus preventing the isFocusTraversableOverridden from being set. This would be a less disruptive change, but I think the more correct way is to call the superclass' methods, as they have additional side effects (setFocusable fires a property change, for example).

Fixes https://youtrack.jetbrains.com/issue/COMPOSE-1398/Make-ComposePanel-transparent-to-accessibility

Testing

Run the app below on Windows, with NVDA turned on, and try traversing the buttons using (ctrl)-shift-tab.
Before this PR, the focus would jump only between the Swing buttons. After it, it will correctly go onto the Compose Button.

fun main() {
    SwingUtilities.invokeLater {
        val frame = JFrame()
        val panel = JPanel(GridLayout(3, 1))
        frame.contentPane.add(panel)

        panel.add(JPanel().apply {
            add(JButton("Swing Button 1"))
        })
        panel.add(ComposePanel().apply {
            setContent {
                Column {
                    Button(onClick = {}) { Text("Compose Button") }
                }
            }
        })
        panel.add(JPanel(GridLayout(2, 1)).apply {
            add(JButton("Swing Button 2"))
        })
        frame.size = Dimension(400, 500)
        frame.isVisible = true
    }
}

This could be tested by QA

Release Notes

Fixes - Desktop

• When using ComposePanel inside a Swing application on Windows with NVDA turned on, focus will now correctly go into the ComposePanel when traversing with (ctrl)-shift-tab.

[igordmn]

Tested on Windows - works as expected with/without NVDA, unit test pass.