fnType

pub fn fnType(
    self: *Builder,
    ret: Type,
    params: []const Type,
    kind: Type.Function.Kind,
) Allocator.Error!Type {
    try self.ensureUnusedTypeCapacity(1, Type.Function, params.len);
    switch (kind) {
        inline else => |comptime_kind| return self.fnTypeAssumeCapacity(ret, params, comptime_kind),
    }
}