Create new API variants that allow to compute the size of a control given a `Monitor`

[laeubi]

A Monitor can have different DPI setting, and some things (e.g. Fonts see here for an example) do not scale linear but SWT currently assume this for scaling.

To account for this, it would be good to have a new method:

Point computeSize (int wHint, int hHint, Monitor monitor)

that can be implemented by a control to account for this (the default method would simply delegate to Point computeSize (int wHint, int hHint)) to allow client code to possibly calculate (and possibly cache) values base on a monitor.