When a nested column is dragged, the column drag header (blue) is positioned wrong. It appears at the very left of the table and not where the column is.
 The fix is to calculate the bound based off the `TableHeaderRow` (and not the parent `NestedTableColumnHeader`. ------------- Commit messages: - JDK-8320444: Column drag header is positioned wrong for nested columns Changes: https://git.openjdk.org/jfx/pull/1292/files Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1292&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8320444 Stats: 78 lines in 3 files changed: 77 ins; 0 del; 1 mod Patch: https://git.openjdk.org/jfx/pull/1292.diff Fetch: git fetch https://git.openjdk.org/jfx.git pull/1292/head:pull/1292 PR: https://git.openjdk.org/jfx/pull/1292