[8u] RFR 8236645: JDK 8u231 introduces a regression with incompatible handling of XML messages

[Elliott Baron]

Hi,

I'd like to request a review of 8236645 for 8u. 8236645 is a bug fix for 
Oracle JDK 8 that I have re-implemented for OpenJDK 8u.

Original fix:
https://bugs.openjdk.java.net/browse/JDK-8236645
CSR:
https://bugs.openjdk.java.net/browse/JDK-8237765

This fixes a regression introduced by 8177334 and 8217878 by introducing 
a new system property 
"com.sun.org.apache.xml.internal.security.lineFeedOnly", which gives 
Base64 encodings in XML digital signatures the same line-ending format 
as before these changes were made. The CSR outlined the behaviour of 
this system property and how it was originally implemented.

I added a new test file for this change, based on test cases in 
javax/xml/crypto/dsig/GenerationTests. This allows us to run the test 
with the property enabled and disabled, and also doesn't interfere with 
future backports affecting GenerationTests.

8u webrev:
https://cr.openjdk.java.net/~ebaron/jdk8u/JDK-8236645/webrev.00/

Testing: x86_64 build, jdk_tier1, jdk_security tests

Thanks,
Elliott