RFR [13] 8217878: ENVELOPING XML signature no longer works in JDK 11

[Sean Mullan]

In JDK 11, we included an updated version of Apache Santuario (which the 
JDK XML Signature implementation is based on) [1]. This contained a 
newer XML marshalling implementation, which has caused a couple of 
serious regressions (this one and JDK-8218629 [2]).

After unsuccessfully trying to patch the current implementation, we 
decided to back it out and restore the previous code, which had been 
very stable for many years. The newer implementation is different in 
subtle ways and doesn't really offer any advantages other than a bit of 
reduction in lines of code. The Apache Santuario Project also has backed 
out the implementation.

webrev: http://cr.openjdk.java.net/~mullan/webrevs/8217878/webrev.00/
bug: https://bugs.openjdk.java.net/browse/JDK-8217878

New test cases have also been added for the regressions.

Note that this also fixes JDK-8218629 [2]. Since technically they are 
different issues, I will probably include both bug-ids in this changeset.

--Sean

[1] https://bugs.openjdk.java.net/browse/JDK-8177334
[2] https://bugs.openjdk.java.net/browse/JDK-8218629