JDK-8371309 changes the end positions reported for synthetic trees.

The following example shows that the end positions reported for synthetic trees like implicit constructors, and the inferred type of `var` variables, changes from -1 before the change to being the same as the start position of the AST node.

Before:

$ java --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED CompilerTest.java
[0,-1]

<init>() {
    super();
}
[27,-1]
int x = 42

After:

$ java --add-exports=jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED CompilerTest.java
[0,0]

<init>() {
    super();
}
[27,27]
int x = 42

Repro:

```
import com.sun.source.tree.CompilationUnitTree;
import com.sun.source.tree.MethodTree;
import com.sun.source.tree.Tree;
import com.sun.source.tree.VariableTree;
import com.sun.source.util.JavacTask;
import com.sun.source.util.TreePathScanner;
import com.sun.tools.javac.tree.JCTree;

import javax.tools.JavaCompiler;
import javax.tools.JavaFileObject;
import javax.tools.SimpleJavaFileObject;
import javax.tools.ToolProvider;
import java.io.IOException;
import java.net.URI;
import java.util.List;

public final class CompilerTest {

  public static void main(final String[] args) throws IOException {
    final JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
    final JavacTask task =
        (JavacTask) compiler.getTask(null, null, null, null, null, List.of(new TestFileObject()));
    final Iterable<? extends CompilationUnitTree> compilationUnitTrees = task.parse();
    task.analyze();
    for (final CompilationUnitTree compilationUnitTree : compilationUnitTrees) {
      var endPosTable = ((JCTree.JCCompilationUnit) compilationUnitTree).endPositions;
      new TreePathScanner<Void, Void>() {
        @Override
        public Void visitMethod(MethodTree node, Void unused) {
          if (node.getName().contentEquals("<init>")) {
            printPosition(node);
            System.err.println(node);
          }
          return super.visitMethod(node, unused);
        }

        @Override
        public Void visitVariable(VariableTree node, Void unused) {
          if (node.getName().contentEquals("x")) {
            printPosition(node.getType());
            System.err.println(node);
          }
          return super.visitVariable(node, unused);
        }

        private void printPosition(Tree tree) {
          JCTree jcTree = (JCTree) tree;
          System.err.printf(
              "[%d,%d]\n", jcTree.getStartPosition(), jcTree.getEndPosition(endPosTable));
        }
      }.scan(compilationUnitTree, null);
    }
  }

  private static final class TestFileObject extends SimpleJavaFileObject {

    public TestFileObject() {
      super(URI.create("myfo:/Test.java"), JavaFileObject.Kind.SOURCE);
    }

    @Override
    public CharSequence getCharContent(final boolean ignoreEncodingErrors) throws IOException {
      return """
          class T {
            void f() {
              var x = 42;
            }
          }
          """;
    }
  }
}

```