`T.infinity` aborted with an internal `LOG(FATAL)` ("Cannot decide
infinity for type float8_e5m2") because `infinity_op` had no fp8 branch.
e5m2 is the only fp8 format with a representable inf, so add a branch
returning +inf, and emit it in codegen via its bit pattern
(`::bitcast(0x7c)`, mirroring the tfloat32 path) since inf/NaN cannot be
spelled as a float literal for the fp8 constructor. Other fp8 formats
(e4m3*, e3m4, e8m0, finite fnuz incl. e5m2fnuz) have no inf and keep the
fatal. Adds e5m2 to the infinity test.
Xuyang Li
d36ec37c59