Change name of "pointSet"

[OAGr]

We use the name "pointSet" a lot, as discussed here:
https://www.squiggle-language.com/docs/Discussions/Three-Types-Of-Distributions

However, this is not a common name, and can easily get confused with sampleSet.

For those not used to Squiggle, a "Point Set" distribution format is a list of x-y coordinates that represents the shape of a distribution.

This format can be used for pdfs now, but later I imagine it could also be used for cdfs.

It would be good to change this soon, especially before Sage starts using Squiggle.

Some ideas:

1. pointShape
2. pdfShape
3. pdfPoints
4. discretisedShape
5. graph
6. xyCoord

[Platinuman]

Another idea:
model, dataSet, sampleSet

No strong preferences besides not using pdf* if its also used for cdfs