Focus the dialog instead of the first item

[patricia-gallardo]

Fix #773

Focus the dialog if there are noe autofocus items available, instead of picking the first focusable item

[chaals]

Needs to be tested - this is based on the agreement in #773 (and likewise in related whatwg/html#1929) and predecessors from bugzilla

[LJWatson]

Test case from MDN, and support data from CIU

Test: when a <dialog> element is opened and the dialog does not contain a field with autofocus enabled, is keyboard focus placed on the <dialog> element itself?

Chrome desktop/mobile: no
Edge: dialog not supported
Firefox: ? (supported behind a flag)
IE: dialog not supported
Opera Mini: dialog not supported
Safari desktop/mobile: dialog not supported
Samsung Internet: no
UC Browser: ?

[patricia-gallardo]

Tested on Linux:
Chromium (Chrome/Vivaldi/Opera) all focus the dropdown
Firefox (after enabling in about:config dom.dialog_element.enabled) does not focus anything
I have not tested in Webkit (no mac) or Edge (no windows)
Both Webkit and Edge have issues open around the dialog element, however the support for the element still seems to be in its early stages.

[chaals]

Looks good. Note that the change is at risk because there is only one implementation at the moment.