[core] Fix XMLRenderer newlines when running under IBM Java

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Describe the PR

When running PMD under Windows with IBM's Java, then the produced XML report looks like this:

<?xml version="1.0" encoding="UTF-8"?>&#xD;
<pmd xmlns="http://pmd.sourceforge.net/report/2.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://pmd.sourceforge.net/report/2.0.0 http://pmd.sourceforge.net/report_2_0_0.xsd" version="6.28.0" timestamp="2020-10-15T10:24:55.318">&#xD;
</pmd>&#xD;

IBM's Java obviously uses an interesting implementation for XMLStreamWriter. The produced XML is invalid, e.g. xmllint says this:

$ xmllint out.xml
out.xml:1: parser error : Start tag expected, '<' not found
<?xml version="1.0" encoding="UTF-8"?>&#xD;

This problem exists since I've refactored XMLRenderer to use XMLStreamWriter with PMD 6.26.0 (see #2633).

Testing is a bit complicated, but possible under Linux (originally, this problem appears only under Windows, due to different default line separators). In order to test it, you'll need

1. IBM's Java 8 SDK -> https://www.ibm.com/support/pages/java-sdk-downloads-version-80
2. The following start script for PMD for some bash magic...

#!/bin/bash

PMD_DIR=~/PMD/pmd-bin-6.28.0
#PMD_DIR=~/PMD/pmd-bin-6.29.0-SNAPSHOT

PMD_JAVA_OPTS=-Dline.separator=$'\r\n'
LIB_DIR=$PMD_DIR/lib

# need to source run.sh, otherwise subshell is used and IFS is not inherited and contains $'\n'
# which will destroy line.separator property (PMD_JAVA_OPTS is word split at the newline char)
IFS=' '
source $PMD_DIR/bin/run.sh pmd -f xml -d . -R rulesets/java/quickstart.xml -no-cache

Other changes

This PR also adds the missing call to "writeEndDocument()".

Related issues

• [core] Fix XMLRenderer encoding issues #2633
• [core] PMD/CPD produces invalid XML (insufficient escaping/wrong encoding) #2615
• See also https://stackoverflow.com/questions/29675481/xmlstreamwriter-java-8-writecharacters-xd

Ready?

• Added unit tests for fixed bug/feature
• Passing all unit tests
• Complete build ./mvnw clean verify passes (checked automatically by travis)
• Added (in-code) documentation (if needed)

[pmd-test]

	1 Message
📖	This changeset introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 0 errors and 0 configuration errors. Full report
✅	This changeset introduces 0 new violations, 0 new errors and 0 new configuration errors, removes 0 violations, 0 errors and 0 configuration errors. Full report

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