Moves to Java11 and OpenJDK via AdoptOpenJDK within the processing4 train.

Moves to Java11 and OpenJDK via AdoptOpenJDK within the processing4 train using a squash of sampottinger processing fork's java11 branch.

**Primary required changes:**
Some changes directly support OpenJFX / OpenJDK 11:

 - Response to image loading changes caused by [JEP 320](https://openjdk.java.net/jeps/320)
 - Use of jmodules as necessitated by [JEP 261](https://openjdk.java.net/jeps/261)
 - Reponse to largely changed file paths caused by [JEP 220](https://openjdk.java.net/jeps/220).
 - Modifications in build system related to AdoptOpenJDK and Java 11 which have a different naming structure for downloads.
 - Allowing use of non-Oracle Java within internal Processing checks.

**Secondary required changes:**
There were some secondary required changes that impacted the usability of Processing after having moved to OpenJFX / OpenJDK 11:

 - Removal of com.apple.eawt calls related to [JEP 272](http://openjdk.java.net/jeps/272)
 - Response to HiDPI support on Windows and Linux in [JEP 263](https://openjdk.java.net/jeps/263)
- Removal of `java.ext.dirs`. Would be forced by [JEP 220](http://openjdk.java.net/jeps/220).
 - Due to bugs on Windows, updated the JNA jars.
 - Changes in downloader build tasks to support AdoptOpenJDK and OpenJFX.
 - Updated org.eclipse.* / equinox jars.
 - Some optimization around size of distribution.
 - Update of AppBundler.
 - Some changes in formulation of classpath and modifications in PreprocessingService given [JEP 261](https://openjdk.java.net/jeps/261).

**Incidental changes:**
This was (ahem) a bit of a larger PR with the above modifications. So, I wanted to introduce automated tests when possible and convenient along with a few changes for platform sustainability in order to support development:

 - Addition of cross-building capability (!) made possible by AdoptOpenJDK.
 - Addition of mockito for testing.
 - Upgrade of junit.
 - Addition of ant-contrib.
 - Standardized nomenclature around JRE / JDK in `build/build.xml`
 - Deduplication of code in `jre/build.xml`.
 - Addition of JavaDoc in a few places.
 - Some refactoring of PImage / Shape to support increased testing and readability in image manipulation code.

java/mode/plugin.properties

@@ -0,0 +1,34 @@
+###############################################################################
+# Copyright (c) 2000, 2014 IBM Corporation and others.
+#
+# This program and the accompanying materials
+# are made available under the terms of the Eclipse Public License 2.0
+# which accompanies this distribution, and is available at
+# https://www.eclipse.org/legal/epl-2.0/
+#
+# SPDX-License-Identifier: EPL-2.0
+#
+# Contributors:
+#     IBM Corporation - initial API and implementation
+#     Harry Terkelsen (het@google.com) - Bug 449262 - Allow the use of third-party Java formatters
+###############################################################################
+providerName=Eclipse.org
+pluginName=Java Development Tools Core
+javaNatureName=Java
+javaBuilderName=Java Builder
+javaProblemName=Java Problem
+buildPathProblemName=Build Path Problem
+transientJavaProblemName=Transient Java Problem
+classpathVariableInitializersName=Classpath Variable Initializers
+classpathContainerInitializersName=Classpath Container Initializers
+codeFormattersName=Source Code Formatters
+compilationParticipantsName=Compilation Participants
+annotationProcessorManagerName=Java 6 Annotation Processor Manager
+javaTaskName=Java Task
+javaPropertiesName=Java Properties File
+javaSourceName=Java Source File
+javaClassName=Java Class File
+jarManifestName=JAR Manifest File
+traceComponentLabel=JDT Core
+javaFormatterName=Java Formatter
+defaultJavaFormatterName=Eclipse [built-in]