[FEATURE]: Setting `itemheight` (analogous to `itemwidth`) to increase height of fill in legend

Description

Please consider adding layout.legend.itemheight setting (similar to current layout.legend.itemwidth)

For plots with a fillpattern applied, it would be great if we could increased the height of the corresponding legend item so that more of the fill pattern was visible.

Why should this feature be added?

Currently, the fillpattern is only 6 pixels high (I think), but if we could make it higher then more of the pattern would be visible.

Mocks/Designs

The current legend item height:

Setting the svg path to v12 shows more of the pattern fill and makes the regions more easily identifiable (my vertical alignment is off, but hopefully the concept is clear enough).

Best regards