Output zig targets as ZON instead of JSON (#22939)

* Adds startTupleField/startStructField, makes pattern in print targets less verbose

* Makes some enums into strings

* Start/finish renamed to begin/end

I feel bad changing this, but I don't know why I named them this way in the first place.
Begin/end is consistent with the json API, and with other APIs in the wild that follow this pattern.
Better to change now than later.

Author: MasonRemaley