chore: update projection/field access wording

[robsimmons]

Following up from a conversation with @david-christiansen about "field projection" being confusing in the case of generalized field notation.

Proposed guideline:

Generalized field notation does not introduce new projections: a.x is (generalized) field notation, a.1 is a projection or projection notation. If .x is an invocation of a function that is not a part of the structure, then it is a, .x is a field access. If x is an actual declared part of the structure that could equivalently be projected with projection notation, then .x may be referred to as a projection or field projection. (Field access is the more general term.)

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