Number followed by identifier should be a parse error

[raffopazzo]

The following is currently accepted because 0 gets parsed as a separate token from int32_t. It would be less surprising if it instead was rejected.

func f(0i32_t x) -> i32_t { return 0; }

It might also be worth reviewing if the same happens with other kinds of tokens.

[raffopazzo]

For avoidance of doubt, this should not apply to punctuation, eg 0,0,0,0, and i32_t,i32_t,i32_t should both be accepted.