2173: MBE: Add TokenId shift in macro_rules r=matklad a=edwin0cheng
As discussed in #2169 , for fixing duplication TokenId during expansion :
> What we can do here is to re-number the tokens during expansion. Specifically:
> * when we create macro_rules, we note the highest id of the token we have as shift>
> * when we expand macro rules, if we need to output a token from definition, we just re-use its id
> * if we need to output a token from the argument, we increase its id by shift (so it's guaranteed to not to collide with anything from the definition)
> * finally, when we have a HirFileId of the expansion, we can look up the original value of shift and classify node to the arg/def by comparing it's id with shift.
>
This PR implement first 3 points of above solution.
Co-authored-by: Edwin Cheng <edwin0cheng@gmail.com>
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