Projects with `:` in their name break JUnit test execution on MacOS (and probably all Unix/Linux OSes)

Steps to reproduce:
1. Create Java project with name "`foo:bar`"
2. Create JUnit test `some.JUnitTestClass` inside project
3. Right click JUnit test and select _Run As > JUnit Test_

Observe the following error in Console:
```
Class not found some.JUnitTestClass
java.lang.ClassNotFoundException: some.JUnitTestClass
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:581)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.loadClass(RemoteTestRunner.java:766)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.loadClasses(RemoteTestRunner.java:490)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:513)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:756)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:452)
at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:210)
```

The reason is that on these platforms the path separator jar is a colon `:`.

If you look into the generated command line call you can see that the `-classpath` is setup with these colons:
```
-classpath "/Users/.../workspace/foo:bar/bin:...
```

To the JVM these are separate classpath entries.

I think to continue supporting `:` in project names the classpath must be provided by a classpath jar.

Reproduce the failure with a Java project named `foo:bar` and inspect the generated JUnit command line, especially the `-classpath` value. Read the `RemoteTestRunner` path shown in the stack trace and trace where the classpath is assembled. Done means the named JUnit test runs successfully on Unix-like systems when the project name contains `:`.

Written by the indexing model from the issue text.