This PR introduces support for `FPEncoding` operand for SPIR-V
instruction `OpTypeFloat`, with the following main changes:
1. Introduces `FPEncoding` enum class to represent floating-point
encodings, such as `BFloat16KHR`, in SPIR-V.
2. Updates SPIR-V instruction `OpTypeFloat` to accept `FPEncoding` as
its second input operand.
3. Updates SPIR-V type creation to handle new encoding requirements.
This PR enables support for the BFloat floating-point type in SPIR-V.
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