Add Markdown support (JEP 467) for Java 23.

[rgrunber]

• Delegate to markdown content access when javadoc node starts with '///'
• Add basic testcase

A continuation of #3278 .

Note : Links currently don't work. I did try to define a private static class JdtLsMarkdownAccessImpl extends CoreMarkdownAccessImpl that copies over the link creation from

eclipse.jdt.ls/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/javadoc/JavadocContentAccess2.java

Lines 308 to 322 in 12b4cbc

	protected String createLinkURI(String scheme, IJavaElement element, String refTypeName, String refMemberName, String[] refParameterTypes) throws URISyntaxException {
	URI javadocURI = CoreJavaElementLinks.createURIAsUri(scheme, fElement, refTypeName, refMemberName, refParameterTypes);
	IJavaElement linkTarget = CoreJavaElementLinks.parseURI(javadocURI);
	if (linkTarget == null) {
	return "";
	}
	try {
	Location locationToElement = JDTUtils.toLocation(linkTarget);
	if (locationToElement != null) {
	return locationToElement.getUri() + "#" + (locationToElement.getRange().getStart().getLine() + 1);
	}
	} catch (JavaModelException e) {
	}
	return "";
	}

. It doesn't seem to work because markdown links seem to be converted to the form <code><a href="[url]">[label]</a></code> and Remark doesn't seem to like preserving links within <code> blocks.