RFR: 8232943: Gesture support is not initialized on iOS

[Jose Pereda]

This PR only affects iOS native code.

JBS issue: https://bugs.openjdk.java.net/browse/JDK-8232943

Since the `IosGestureSupport` class is only instantiated from the native side, the proposal is to change in `ios/GlassViewDelegate.m` the use of `FindClass` in favor of `[GlassHelper ClassForName]`, in the same way as it is done in [`mac/GlassViewDelegate.m`](https://github.com/openjdk/jfx/blob/master/modules/javafx.graphics/src/main/native-glass/mac/GlassViewDelegate.m#L614) to instantiate `MacGestureSupport`.

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Commits:
 - 49f39910: Use ClassForName instead of FindClass

Changes: https://git.openjdk.java.net/jfx/pull/23/files
 Webrev: https://webrevs.openjdk.java.net/jfx/23/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8232943
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/23.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/23/head:pull/23

PR: https://git.openjdk.java.net/jfx/pull/23