RFR: 8196587: Remove use of deprecated finalize method from JPEGImageLoader

[Ambarish Rapte]

The finalize() method is deprecated in JDK9. See [Java 9 deprecated features](https://www.oracle.com/technetwork/java/javase/9-deprecated-features-3745636.html).
And so the JPEGImageLoader.finalize() method should be removed.

The change is,
1. Remove finalize method from JPEGImageLoader class.

2. Instance of JPEGImageLoader is created and used in ImageStorage class. JPEGImageLoader.dispose() should be called after it's use over. This would be a common call for the other (GIF, PNG, BMP) ImageLoader classes, which have empty dispose() method.

3. JPEGImageLoader.load() method almost always calls the dispose() method after the image is loaded. In normal scenario JPEGImageLoader is disposed here. The calls to dispose() added in ImageStorage seem logically correct place to add and should be added.

Verification:
Verified :graphics:test and system tests on all three platforms.
Verified that JPEGImageLoader.dispose() is always initiated by JPEGImageLoader.load()

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Commits:
 - b48c8087: 8196587: Remove use of deprecated finalize method from JPEGImageLoader

Changes: https://git.openjdk.java.net/jfx/pull/50/files
 Webrev: https://webrevs.openjdk.java.net/jfx/50/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8196587
  Stats: 28 lines in 2 files changed: 14 ins; 12 del; 2 mod
  Patch: https://git.openjdk.java.net/jfx/pull/50.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/50/head:pull/50

PR: https://git.openjdk.java.net/jfx/pull/50