Since surrogate pairs are internally considered as 2 characters and text field is null in `HitInfo` when `getInsertionIndex` is invoked from `TextFlow`, wrong insertion index was returned.
Updated code to calculate insertion index in `getHitInfo` method of `PrismTextLayout` class when `hitTest` of trailing side of surrogate pair is requested. Since text runs are processed in this method already, calculating the insertion index in this method looks better than calculating in `getInsertionIndex` of `HitInfo` method. The latter approach also requires the text to be sent to `HitInfo` as parameter from the `hitTest` method of `TextFlow`. If the number of `Text` nodes in `TextFlow` are very large, processing all the `Text` nodes on each `hitTest` method invocation might cause performance issue. Hence implemented first approach. Added system test to validate the fix. ------------- Commit messages: - Fix insertion index calculation issue in TextFlow Changes: https://git.openjdk.org/jfx/pull/1091/files Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1091&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8304831 Stats: 182 lines in 2 files changed: 181 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jfx/pull/1091.diff Fetch: git fetch https://git.openjdk.org/jfx.git pull/1091/head:pull/1091 PR: https://git.openjdk.org/jfx/pull/1091
