Fix List Filter Menu is not accessible

[WiXSL]

Fixes #6964

[djhi]

While you're on this file, would you mind adding the missing aria-haspopup="true" on the Button element?

[djhi]

I don't get why this is necessary to fix the keyboard navigation. Can you explain?

[WiXSL]

I couldn't get it to work otherwise, I'm forcing the focus on the first menu item, do you have a suggestion with aria attributes?

[djhi]

No but I fail to find a difference between our code and the MUI v4 demos for the menu

[WiXSL]

No but I fail to find a difference between our code and the MUI v4 demos for the menu

What I've noticed is that they don't have a forwardRef MenuItem inside a Menu in their examples.
The keyboard navigation works out of the box without this, but of course, we need it because of the use of FilterButtonMenuItem.

For example, this works (without the use of FilterButtonMenuItem):

// FilterButton.jsx
...
<Menu
    open={open}
    anchorEl={anchorEl.current}
    onClose={handleRequestClose}
>
    {hiddenFilters.map((filterElement: JSX.Element, index) => (
        <MenuItem
            key={filterElement.props.source}
            data-key={filterElement.props.source}
            data-default-value={filterElement.props.defaultValue}
            onClick={() =>
                handleShow({
                    source: filterElement.props.source,
                    defaultValue: filterElement.props.defaultValue,
                })
            }
        >
            <FieldTitle
                label={filterElement.props.label}
                source={filterElement.props.source}
                resource={resource}
            />
        </MenuItem>
    ))}
</Menu>
...

Of course, it would be a BC.
Now, why does it work when not using a forwardRef ?, I don't know.