Use new Unicode 13 Symbols for Legacy Computing for the visualizations

[rbanffy]

Unicode 13 provides 213 new symbols (https://www.unicode.org/charts/PDF/U1FB00.pdf) that can be used for bar and area charts and to complement the Braille characters for line and text drawing. Many of these characters are supported directly by some terminals (VTE, at least) without the need for a font. Sampler should use them.