We already have a CoordCache of insets dimensions. It is not necessary
to store the same information in two places.
Give a name to CoordCache tables types to improve code readability.
Remove ParagraphMetrics::singleWidth, which is not used anymore.
This is a work in progress intended to start collective work towards improving the performance of our painting process.
The intent is to make it a living document that is updated as code evolves.
