Consolidate grammar to decrease complexity for other UpSet implementations

[JakeWags]

Alt Text:

"We are accessing rawData["sets"], particularly for each set in rawData["sets"], we are accessing ["elementName"], rawData["sets"]["size"], then rawData["items"] and rawData["setColumns"]"

The grammar should be consolidated so that the alt text generator can remove any usage of rawData. This is because many (if not all) other UpSet implementations will not have the same data access as multinet provides for UpSet 2.

In doing this, adding a grammar and alt-text generator to other versions of UpSet will be simpler and easier for authors/contributors.

[JakeWags]

tasks:

• [ ] add "visible" flag to processedData