encoding/xml: simplify slice-growing logic in rawToken
It appears that old code (from 2009) in xml.(*Decoder).rawToken
replicates append's slice-growing functionality by allocating a new,
bigger backing array and then calling copy.
Simplifying the code by replacing it with a single append call does
not seem to hurt performance:
name old time/op new time/op delta
Marshal-4 11.2µs ± 1% 11.3µs ±10% ~ (p=0.069 n=19+17)
Unmarshal-4 28.6µs ± 1% 28.4µs ± 1% -0.60% (p=0.000 n=20+18)
name old alloc/op new alloc/op delta
Marshal-4 5.78kB ± 0% 5.78kB ± 0% ~ (all equal)
Unmarshal-4 8.61kB ± 0% 8.27kB ± 0% -3.90% (p=0.000 n=20+20)
name old allocs/op new allocs/op delta
Marshal-4 23.0 ± 0% 23.0 ± 0% ~ (all equal)
Unmarshal-4 189 ± 0% 190 ± 0% +0.53% (p=0.000 n=20+20)