[llvm] [mlir] [MLIR] Add f6E3M2FN type (PR #105573)

[Stella Laurenzo via llvm-commits]

stellaraccident wrote:

Just curious as there have been various conversations: have we found a use case for the scalar form of f6 yet? When I've drilled in before, it seemed like there might be a case for that but all uses in the wild I could see were for the shared exponent forms (which are definitely not a scalar type).

https://github.com/llvm/llvm-project/pull/105573