Extra padding for xfwm to assist resizing

Xfce has an issue with resizing, as the resize icon will only appear when it touches the pixels of the window border. Presently that means it will only appear when touching the 2 pixels found on the left, right and bottom parts of the window. Please increase the size to 5 pixels, with the additional 3 pixels taking the color of the internal window background.

You can see how this is done in the Default-hdpi window manager theme compared to the Default theme.

Compare the Default-hdpi window manager theme with the Default theme to find how their resize padding is defined. Update the relevant theme styling so the left, right, and bottom areas are 5 pixels wide, with the extra 3 pixels using the internal window background color. Done means the resize icon appears before touching the border pixels.

Written by the indexing model from the issue text.