Add icon blit helper function

[riknoll]

Adds a helper method for using the blit function with icons.

Icons in arcade are 1 bit per pixel, so they don't contain any color information. Our other icon methods take a color argument to use for the non-transparent pixels; this simply adds a copy of blit that passes such an argument.

I need this for my fancy-text extension (or, rather, for my mini-menu extension which I am converting to use the fancy-text extension).

[eanders-ms]

LGTM! Conditionals in the inner loop aren't ideal, but something we can optimize later if the need arises.

[jwunderl]

LGTM, as eric said bit of a hotpath so maybe worth quick hardware tests to double check but can defer that till later too