addTypeExtraAssumeCapacity

fn addTypeExtraAssumeCapacity(self: *Builder, extra: anytype) Type.Item.ExtraIndex {
    const result: Type.Item.ExtraIndex = @intCast(self.type_extra.items.len);
    const info = @typeInfo(@TypeOf(extra)).@"struct";
    inline for (info.field_names, info.field_types) |field_name, field_type| {
        const value = @field(extra, field_name);
        self.type_extra.appendAssumeCapacity(switch (field_type) {
            u32 => value,
            String, Type => @backingInt(value),
            else => @compileError("bad field type: " ++ field_name ++ ": " ++ @typeName(field_type)),
        });
    }
    return result;
}