RFR: 8337656 iOS WebView Position

[Florian Kirmaier]

Fixing WebView on iOS
(I couldn't compile it because I don't know how to build it for iOS, but the code should be correct.)

@johanvos 
If this looks reasonable to you, can you provide a test build for @dlemmermann ?
Then he can test it with his JFX-Central iOS version.

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Commit messages:
 - JDK-8337656-ios-webview-position
 - JDK-8337656-ios-webview-position

Changes: https://git.openjdk.org/jfx/pull/1526/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1526&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337656
  Stats: 9 lines in 1 file changed: 1 ins; 5 del; 3 mod
  Patch: https://git.openjdk.org/jfx/pull/1526.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1526/head:pull/1526

PR: https://git.openjdk.org/jfx/pull/1526