Make OpenROAD-flow-script's `save_image.tcl` part of OpenROAD core

[mithro]

Description

OpenROAD-flow-scripts has a pretty nice save_image.tcl script which makes nice looking images. As many people are likely to want to create nice images, it would be nice if this was wrapped in a function and provided to anyone using OpenROAD.

Suggested Solution

Move the function into the OpenROAD core. Maybe as something like save_pretty_image command available to anyone.

Additional Context

No response