Un-deprecate PathResource (for NIO Path resolution in createRelative)

Includes aligned createRelative signature and dedicated java.io.File test.

Closes gh-24211

spring-core/src/test/java/org/springframework/core/io/ResourceTests.java

@@ -17,6 +17,7 @@
 package org.springframework.core.io;
 
 import java.io.ByteArrayInputStream;
+import java.io.File;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
@@ -130,6 +131,14 @@ class ResourceTests {
 		assertThat(resource).isEqualTo(new FileSystemResource(file));
 	}
 
+	@Test
+	void fileSystemResourceWithFile() throws IOException {
+		File file = new File(getClass().getResource("Resource.class").getFile());
+		Resource resource = new FileSystemResource(file);
+		doTestResource(resource);
+		assertThat(resource).isEqualTo(new FileSystemResource(file));
+	}
+
 	@Test
 	void fileSystemResourceWithFilePath() throws Exception {
 		Path filePath = Paths.get(getClass().getResource("Resource.class").toURI());