Fix NoSuchMethodError happening on JDK 21 (fixes #885) (#886)

The JDK internal class JCImport has changed recently. In JDK 17, the method was defined as:

public JCTree getQualifiedIdentifier() { return qualid; }
and in JDK 21:

public JCFieldAccess getQualifiedIdentifier() { return qualid; }

One possibility to fix that would be to fix the getSimpleName() method to use an argument of type com.sun.source.tree.ImportTree and call the getQualifiedIdentifier() method which returns a com.sun.source.tree.Tree and has not changed.

palantir-java-format/src/main/java/com/palantir/javaformat/java/RemoveUnusedImports.java

@@ -241,7 +241,7 @@ private static RangeMap<Integer, String> buildReplacements(
         return replacements;
     }
 
-    private static String getSimpleName(JCImport importTree) {
+    private static String getSimpleName(ImportTree importTree) {
         return importTree.getQualifiedIdentifier() instanceof JCIdent
                 ? ((JCIdent) importTree.getQualifiedIdentifier()).getName().toString()
                 : ((JCFieldAccess) importTree.getQualifiedIdentifier())