Improve Control#setBounds to deal with rounding errors

[HeikoKlare]

Tracking ticket for:

• [Win32] Make Control bounds point/pixel conversion cope with rounding eclipse-platform/eclipse.platform.swt#2782

Part of:

• Too small/large/cut-off controls at zoom != 100% due to rounding in Control#setBounds() and Composite#getClientArea() #518

[HeikoKlare]

Due to issues with the original PR that I still need to analyze, I extracted the major (and more important) part out of it, which does not seem to cause any issues:

• [Win32] Fix control bounds exceeding parent size eclipse-platform/eclipse.platform.swt#2849

I will meanwhile proceed with analyzing the issue with the remaining part of the original PR.