Represents an (optionally) multi-line block of text of a specified width and number of visible rows at a specified lineHeight
If the supplied text string is longer, only the last displayRows will be shown rendered and sent to Frame.
If the supplied text string has fewer than or equal to displayRows, only the number of actual rows will be rendered and sent to Frame
If any given line of text is shorter than width, the text Sprite will be set to the actual width required.
When sending TxTextSpriteBlock to Frame, the sendMessage() will send the header with block dimensions and line-by-line offsets
and the user then sends each line[] as a TxSprite message with the same msgCode as the Block, and the frame app will use the offsets
to place each line. By sending each line separately we can display them as they arrive, as well as reducing overall memory
requirement (each concat() call is smaller)
