[@sheet] Shadow DOM stylesheet inheritance

[dead-claudia]

Given a hierarchy of global root G > a shadow root A > shadow root B, if a stylesheet with @sheet foo is added to G and a different @sheet foo added to A, how should they compose as adopted by B?

Related: #900, #933, #935, #937, #938 (about half of the existing @sheet-related issues)

This issue leads me more in favor of an HTML-based solution, FWIW.

[dead-claudia]

My suggested resolution is this: do not inherit. Instead, use adopted stylesheets and/or shadowrootstyleorder="outer adopted"/styleOrder: "outer adopted" from w3c/csswg-drafts#11547 to expose them.