Add LM AD transformation for map

[toelli-msft]

See https://github.com/microsoft/knossos-ksc/pull/727

[awf]

What is required? A linear map lmdiag? We do need this to compare with SUF.

[toelli-msft]

Yes, some sort of linear map primitive to express the derivative of map, as discussed at https://github.com/microsoft/knossos-ksc/issues/714. Then we need to implement it in the backend as well.

• [ ] Linear map primitive to express derivative of map
• [ ] Linear map derivative helper primitives
• [ ] Opt rules translating apply of linear map primitive to helper primitives
• [ ] Back end implementation of helper primitives

This is the same strategy as used for fold.

[toelli-msft]

(My strategy for implementing this will approximately be to copy what I did for fold)