ClassNotFoundException in XML Editor

[persicsb]

Describe the bug
While editing XML files with Spring Tool Suite 4 installed with the Spring XML Namespace Support plugin, an error pops up with "error loading referenced grammars" using Java 11.

To Reproduce

1. Use any supported JDK.
2. Open any XML file with STS4 installed.
3. Try to edit the file.

Log

Eclipse logs the following:
java.lang.ClassNotFoundException: org.eclipse.jdt.core.IElementChangedListener cannot be found by org.springframework.ide.eclipse.xml.namespaces_4.11.0.202106180910

I suspect it is a Java Module System issue.

[martinlippert]

I think I saw this error before, but I can't get it to show up here at the moment. Would it be possible to setup a small sample project that reproduces this problem and describe a few steps to reproduce this?