Don't consume token when returning `error.InvalidType`.

[LordMZTE]

Sometimes, it's necessary to deserialize data where the type is uncertain. I tried doing this by first calling deserializeString, and if that returns an InvalidType error, I call deserializeMap. This doesn't work tho, since deserializeString will consume a token from the TokenStream, making it basically unusable afterwards.

[ibokuri]

This would be very helpful, indeed now that I think about it.

However, Serde's able to avoid consuming tokens upon failure because it has a peek operation in its JSON parser. But as far as I know, there's no way to peek at the next token with std.json.TokenStream. The only ways I can think of are:

• Make a copy of the tokens, which we can use later on to restore the tokens.
  • Getty JSON already does this in a few places, but I don't really like it. I can't remember if the copy was expensive or not, but it just looks/feels gross.
• Add a peek method to std.json.TokenStream.
  • This would be ideal imo. But std.json's parser scares me so I haven't looked too deeply into this.
• Implement parsing ourselves, like Serde does.
  • Obviously, this would be a lot of work. And if possible, I would like to avoid changing parsers until everything else in the library is relatively stable.

[ibokuri]

update: A PR for a peek method in std.json has been made: ziglang/zig#12798