Settings: Allow Wi-Fi network details rows to be focusable for a11y

The selectable=false configuration on the underlying Preference items
for the Wi-Fi network details rows makes these rows not be focusable by
keyboard or by TalkBack. Removing this spec allows them to be
accessible. Also verified that the long-press/right-click copy still
works as expected.

Bug: 402241322
Test: Manual. Screen recording in bug comments.
Flag: EXEMPT bugfix
Change-Id: Ie564a23586508cfb65a080a16436a4ace2051e60