Fix Themes v3 not working on Safari

Changes

Basically use <style> elements to replace document.adoptedStyleSheets if it is not available.

Note that this means that we are not able to use the advantage of the separation between eager and lazy styles.

In Safari I am also unable to clone the <style> element and keep its sheet property at the same time, so the style is modified in place.

Closes #1319 (closed)

added Regression needs-review labels

requested review from @hj

merged

mentioned in commit 4c3e2979