Be consistent about touch point id type: use qint32
There is no point in using quint32 and casting back and forth in numerous places.
Fix a bunch of compiler warnings that we implicitly cast between signed and unsigned.
This makes things consistent with what we get from libinput.
Reviewers: KWin, romangg
Reviewed By: KWin, romangg
Subscribers: zzag, romangg, kwin
Differential Revision: https://phabricator.kde.org/D23086