Escape and unescape strings in the parser and printer so they can roundtrip,

print floating point in a structured form that we know can round trip,
enumerate attributes in the visitor so we print affine mapping attributes
symbolically (the majority of the testcase updates).

We still have an issue where the hexadecimal floating point syntax is reparsed
as an integer, but that can evolve in subsequent patches.

PiperOrigin-RevId: 208828876