RFR: 8262802: Wrong context origin coordinates when using EGL and HiDPI

[Jose Pereda]

See [issue](https://bugs.openjdk.java.net/browse/JDK-8262802) for detailed description. 

This PR solves the wrong calculations of ContextX and ContextY in ES2SwapChain when EGL is used on HiDPI devices, by using properly scaled dimensions. Without these changes, any popup control is misplaced.

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Commit messages:
 - Use scaled dimensions to determine the origin coordinates when using EGL

Changes: https://git.openjdk.java.net/jfx/pull/416/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=416&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262802
  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jfx/pull/416.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/416/head:pull/416

PR: https://git.openjdk.java.net/jfx/pull/416