This CL adds missing Instant-based methods to FileTime in J2ObjC JRE emulation to satisfy symbol resolution during transpilation of apache_commons_io.

Context: yaqs/4512214300974120960

This can unblock users from adding a j2objc version of apache_commons_io through external annotations (see https://fusion2.corp.google.com/invocations/acf259d0-e208-4c8a-89da-442f24d83f05).

PiperOrigin-RevId: 896703197

Author: j2objc-copybara

jre_emul/Classes/java/nio/file/attribute/FileTime.java

@@ -17,6 +17,7 @@
 
 package java.nio.file.attribute;
 
+import java.time.Instant;
 import java.util.concurrent.TimeUnit;
 
 /**
@@ -52,6 +53,14 @@ public static FileTime fromMillis(long value) {
     return new FileTime(value);
   }
 
+  public Instant toInstant() {
+    return Instant.ofEpochMilli(millis);
+  }
+
+  public static FileTime from(Instant instant) {
+    return new FileTime(instant.toEpochMilli());
+  }
+
   @Override
   public int compareTo(FileTime o) {
     if (o.millis < millis) {