UAX #14 for line-breaking with quotation marks

In Chinese, “ is an opening quotation mark, but in some languages (like German) it can be a closing quotation mark. In UAX #14:

LB19 Do not break before or after quotation marks, such as ‘ ” ’.

This is too strict for Chinese, because breaks before “ should be allowed (it can appear at the line start).

Specs:
In the description for QU in UAX #14:

Some quotation characters can be opening or closing, or even both, depending on usage. The default is to treat them as both opening and closing.
[...]
Note: If language information is available, it can be used to determine which character is used as the opening quote and which as the closing quote. See the information in Section 6.2, General Punctuation, in [Unicode]. In such a case, the quotation marks could be tailored to either OP or CL depending on their actual usage.

And css-text also allows the UA to determine the set of line-breaking restrictions to use, so it allows for this kind of tailoring.

Tests & results:
Interactive test, In Chinese, breaks before “ are allowed.

• Gecko: ✅
• Blink: ✅
• Webkit: ✅

Bug report:
ICU

Start with UAX #14 rule LB19 and the QU description, then compare the linked Chinese interactive test with the ICU pull request #223. Confirm how Chinese quotation marks should be tailored in the CLReq requirements, and consider the work done when the documented behavior matches the expected Chinese line breaks.