Allow @CompileWithTargetClassAccess to work with all classes

Switch from `MethodHandles.privateLookupIn` to a reflection based
approach to that target classes to not need to be explicitly listed.

Closes gh-28580

spring-core-test/src/test/java/org/springframework/aot/test/generator/compile/TestCompilerTests.java

@@ -170,7 +170,7 @@ class TestCompilerTests {
 	}
 
 	@Test
-	@CompileWithTargetClassAccess(classNames = "com.example.PackagePrivate")
+	@CompileWithTargetClassAccess
 	void compiledCodeCanAccessExistingPackagePrivateClassIfAnnotated() throws ClassNotFoundException, LinkageError {
 		SourceFiles sourceFiles = SourceFiles.of(SourceFile.of("""
 				package com.example;