Revert "Remove resolve classpath when fetching a raw classpath (#3531)"

This reverts commit b79bd1d as it
introduces regressions.

Fixes #3534

org.eclipse.jdt.core/model/org/eclipse/jdt/internal/core/PackageFragmentRoot.java

@@ -613,6 +613,7 @@ public IClasspathEntry getRawClasspathEntry() throws JavaModelException {
 
 	IClasspathEntry rawEntry = null;
 	JavaProject project = getJavaProject();
+	project.getResolvedClasspath(); // force the reverse rawEntry cache to be populated
 	Map rootPathToRawEntries = project.getPerProjectInfo().rootPathToRawEntries;
 	if (rootPathToRawEntries != null) {
 		rawEntry = (IClasspathEntry) rootPathToRawEntries.get(getPath());