"Disclosure pattern" should allow root+trigger on same (preceding sibling) element

[tabatkins]

Whether the "summary" is inside the "details" or before it shouldn't really make a difference, and some of the oddbird examples show off exactly that markup pattern. Right now it's required that it be inside, matching details.

Related: tabs vs exclusive accordion really only have a difference in where the currently-shown panel sits - just below the current "active tab" or in the same spot regardless of active tab. Right now the inference rules distinguish them via the above "inside vs preceding sibling" rule, but once we loosen that we'll have to rely on something else.

Given the current layout challenges with doing a tab control with alternating tab/panel/tab/panel markup, I suggest that for v1 the inference rules give any toggle-group'd sequence of disclosures to the accordion pattern, and limit the tabs pattern to "X triggers, followed by X toggle-visibility panels". We can allow both markup patterns to become tabs in v2 when we formalize the pattern hint (and hopefully have the layout controls in Grid to make this viable in the first place).