And replace it by constructors in OperandKind. There's a single optional
parameter function `set_doc` that remains, and didn't justify the whole
OperandKindBuilder concept to exist.
This applies both to the default_member value (which is now determined at
runtime, instead of pre-computed) and the rust_type value (which is
determined in the Operand's ctor, instead of the builder).
This does a lot at once, since there was no clear way to split the three
commits:
- Instruction need to be passed an explicit InstructionFormat,
- InstructionFormat deduplication is checked once all entities have been
defined;
This avoids a lot of dereferences, and InstructionFormat are immutable
once they're created. It removes a lot of code that was keeping the
FormatRegistry around, just in case we needed the format. This is more
in line with the way we create Instructions, and make it easy to
reference InstructionFormats in general.
