RFR: 8340005: Eliminate native access calls from javafx.swing

[Prasanta Sadhukhan]

While implementing [JDK-8339517](https://bugs.openjdk.org/browse/JDK-8339517) to eliminate native access warnings by passing "--enable-native-access" for the three JavaFX modules with native code (javafx.graphics, javafx.media, and javafx.web), it was found  that the Swing interop code in javafx.swing calls a JNI method defined in one of the native graphics libraries (prism-common) directly

This means that even after [JDK-8339517](https://bugs.openjdk.org/browse/JDK-8339517) is fixed, we still get native access warnings when running any test that uses SwingNode.

This fixes the native access warning by making javafx.graphics module call the native JNI and Swing-interop calls the static utility method in javafx.graphics, in this case defined in PlatformImpl

All test.javafx.embed.swing SwingNode tests are running ok without any native warning

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Commit messages:
 - 8340005: Eliminate native access calls from javafx.swing

Changes: https://git.openjdk.org/jfx/pull/1600/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1600&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340005
  Stats: 18 lines in 3 files changed: 10 ins; 2 del; 6 mod
  Patch: https://git.openjdk.org/jfx/pull/1600.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1600/head:pull/1600

PR: https://git.openjdk.org/jfx/pull/1600