Map the dir attribute with selectors the engine can parse

[maurerdietmar]

The bidi rules in the default stylesheet came from Gecko and match through its internal pseudo-classes (:-moz-dir-attr-rtl and friends), which the servo selector parser does not know. It dropped every one of them, so dir="rtl" set no direction and a page could not switch to right-to-left layout at all, even though the layout side fully supports it.

Use the attribute-selector form from the HTML spec's bidi rendering section instead. dir=auto keeps its isolation but not the content-based direction, which needs bidi analysis no selector can express.

WPT results

3 newly passing, 2 newly failing (net +1).

Full diff (5 changed tests)

+ Fail => Pass css/css-align/self-alignment/self-align-safe-unsafe-flex-003.html
+ Fail => Pass css/css-align/self-alignment/self-align-safe-unsafe-grid-003.html
+ Fail => Pass css/css-text/text-align/text-align-match-parent-01.html
- Pass => Fail css/css-text/text-align/text-align-match-parent-05.html
- Pass => Fail css/css-writing-modes/direction-upright-002.html

_{Generated by the WPT workflow.}