8276207: Properties.loadFromXML/storeToXML works incorrectly for supplementary characters

[Anirvan Sarkar]

Hi,

Properties.loadFromXML/storeToXML works incorrectly for supplementary
characters after JDK-8042889[1] was integrated in JDK 9.

Properties.storeToXML now generates incorrect character references for
supplementary characters. This is similar to JDK-8145974[2] which was fixed
in the java.xml module in JDK 9.

Properties.loadFromXML now fails to parse character references for
supplementary characters and throws InvalidPropertiesFormatException.

Sample program which demonstrates these issues is in the JBS[3].

Proposed patch to fix this issue is attached.
JDK Tier 1 tests are all green.
If it looks fine then I will create a pull request based on this.

[1] : https://bugs.openjdk.java.net/browse/JDK-8042889
[2] : https://bugs.openjdk.java.net/browse/JDK-8145974
[3] : https://bugs.openjdk.java.net/browse/JDK-8276207

-- 
Anirvan