Translate mouse coordinates from Wine window

Instead of the parent Window. Tracktion Waveform does some weird things
with its VST2 editor embedding, so with the old approach this would
cause mouse clicks to be offset 27 pixels vertically and one pixel
horizontally.

CHANGELOG.md

@@ -6,6 +6,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic
 Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- Fixed mouse clicks in VST2 editors in **Tracktion Waveform** being offset
+  vertically because of the way Waveform embeds VST2 editors.
+
 ## [3.3.0] - 2020-06-03
 
 ### Added