Content Assist yields NoClassDefFoundError: org/eclipse/text/readers/SubstitutionReader since 3.19.400.v20231212-0628

Hi,

I just updated from the last RC to 4.30, and now content assist (CTRL+SPACE) is broken. The popup appears briefly (for a couple hundred ms), and a fast ENTER keypress can successfully select the default suggestion. When left alone though, an modal error dialog appears stating that "An internal error occurred during: "Computing additional info". OK-ing that, one finds the following stacktrace in the error log:

```
java.lang.NoClassDefFoundError: org/eclipse/text/readers/SubstitutionReader
at java.base/java.lang.ClassLoader.defineClass1(Native Method)
at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.defineClass(ModuleClassLoader.java:283)
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.defineClass(ClasspathManager.java:716)
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findClassImpl(ClasspathManager.java:639)
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findLocalClassImpl(ClasspathManager.java:607)
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findLocalClassImpl(ClasspathManager.java:587)
at org.eclipse.osgi.internal.loader.classpath.ClasspathManager.findLocalClass(ClasspathManager.java:566)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.findLocalClass(ModuleClassLoader.java:335)
at org.eclipse.osgi.internal.loader.BundleLoader.findLocalClass(BundleLoader.java:397)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass0(BundleLoader.java:500)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:416)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:168)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
at org.eclipse.jdt.core.manipulation.internal.javadoc.CoreJavadocAccess.javadoc2HTML(CoreJavadocAccess.java:420)
at org.eclipse.jdt.core.manipulation.internal.javadoc.CoreJavadocAccess.getHTMLContentFromSource(CoreJavadocAccess.java:369)
at org.eclipse.jdt.core.manipulation.internal.javadoc.CoreJavadocAccess.getHTMLContent(CoreJavadocAccess.java:230)
at org.eclipse.jdt.internal.ui.text.javadoc.JavadocContentAccess2.getHTMLContent(JavadocContentAccess2.java:56)
at org.eclipse.jdt.internal.ui.text.java.ProposalInfo.extractJavadoc(ProposalInfo.java:93)
at org.eclipse.jdt.internal.ui.text.java.ProposalInfo.computeInfo(ProposalInfo.java:78)
at org.eclipse.jdt.internal.ui.text.java.ProposalInfo.getInfo(ProposalInfo.java:63)
at org.eclipse.jdt.internal.ui.text.java.AbstractJavaCompletionProposal.getAdditionalProposalInfo(AbstractJavaCompletionProposal.java:582)
at org.eclipse.jface.text.contentassist.AdditionalInfoController$Timer$2$1.run(AdditionalInfoController.java:116)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: java.lang.ClassNotFoundException: org.eclipse.text.readers.SubstitutionReader cannot be found by org.eclipse.jdt.core.manipulation_1.21.0.v20231212-1437
at org.eclipse.osgi.internal.loader.BundleLoader.generateException(BundleLoader.java:541)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass0(BundleLoader.java:536)
at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:416)
at org.eclipse.osgi.internal.loader.ModuleClassLoader.loadClass(ModuleClassLoader.java:168)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:525)
... 24 more
```

Since this has worked recently (with Eclipse Java Development Tools 3.19.300.v20231201-0110, Updated on Dec, 5th 2023), I guess this is a recent regression, first seen (by me) after updating to Eclipse Java Development Tools 3.19.400.v20231212-0628.

```
eclipse.buildId=4.30.0.20231201-1200
java.version=17.0.9
java.vendor=Eclipse Adoptium
BootLoader constants: OS=win32, ARCH=x86_64, WS=win32, NL=de_AT
Framework arguments: -product org.eclipse.epp.package.committers.product -product org.eclipse.epp.package.committers.product -product org.eclipse.epp.package.committers.product -product org.eclipse.epp.package.committers.product
Command-line arguments: -os win32 -ws win32 -arch x86_64 -product org.eclipse.epp.package.committers.product -product org.eclipse.epp.package.committers.product -product org.eclipse.epp.package.committers.product -data file:/C:/Users//development/workspace/ -product org.eclipse.epp.package.committers.product
```

I'll see if I can trace this to a commit if I can find the time later. But maybe I made someone feel a little guilty already ;)

Cheers!