html: avoid copying tag names and attributes without NUL bytes

[thevilledev]

CL 781883 made TagName and TagAttr replace NUL bytes in tag names and
attribute keys and values using bytes.ReplaceAll. ReplaceAll returns a
copy even if there is nothing to replace, so since then every tag name,
attribute key and attribute value is allocated, although they rarely
contain a NUL byte.

Only copy them if they contain a NUL byte, as Text already does.
Otherwise return slices of the tokenizer's buffer, as before CL 781883,
which the documentation of Raw allows.

goos: darwin
goarch: arm64
pkg: golang.org/x/net/html
cpu: Apple M1 Max
│ master.txt │ new.txt │
│ sec/op │ sec/op vs base │
Parser-10 820.1µ ± 0% 761.2µ ± 0% -7.19% (p=0.000 n=10)
RawLevelTokenizer-10 276.3µ ± 0% 277.0µ ± 1% ~ (p=0.190 n=10)
LowLevelTokenizer-10 437.9µ ± 0% 371.0µ ± 1% -15.27% (p=0.000 n=10)
HighLevelTokenizer-10 516.0µ ± 1% 451.1µ ± 2% -12.59% (p=0.000 n=10)
geomean 475.7µ 433.4µ -8.89%

                  │  master.txt  │               new.txt                │
                  │     B/s      │     B/s       vs base                │

Parser-10 90.89Mi ± 0% 97.92Mi ± 0% +7.74% (p=0.000 n=10)
RawLevelTokenizer-10 269.8Mi ± 0% 269.1Mi ± 1% ~ (p=0.190 n=10)
LowLevelTokenizer-10 170.2Mi ± 0% 200.9Mi ± 1% +18.03% (p=0.000 n=10)
HighLevelTokenizer-10 144.4Mi ± 1% 165.2Mi ± 2% +14.40% (p=0.000 n=10)
geomean 156.7Mi 172.0Mi +9.75%

                  │  master.txt   │                new.txt                 │
                  │     B/op      │     B/op      vs base                  │

Parser-10 575.4Ki ± 0% 539.6Ki ± 0% -6.22% (p=0.000 n=10)
RawLevelTokenizer-10 10.23Ki ± 0% 10.23Ki ± 0% ~ (p=1.000 n=10) ¹
LowLevelTokenizer-10 42.29Ki ± 0% 10.23Ki ± 0% -75.80% (p=0.000 n=10)
HighLevelTokenizer-10 128.15Ki ± 0% 92.36Ki ± 0% -27.93% (p=0.000 n=10)
geomean 75.16Ki 47.80Ki -36.40%
¹ all samples are equal

                  │  master.txt  │                new.txt                │
                  │  allocs/op   │  allocs/op   vs base                  │

Parser-10 11.189k ± 0% 7.470k ± 0% -33.24% (p=0.000 n=10)
RawLevelTokenizer-10 678.0 ± 0% 678.0 ± 0% ~ (p=1.000 n=10) ¹
LowLevelTokenizer-10 4397.0 ± 0% 678.0 ± 0% -84.58% (p=0.000 n=10)
HighLevelTokenizer-10 7.094k ± 0% 3.375k ± 0% -52.42% (p=0.000 n=10)
geomean 3.922k 1.845k -52.96%
¹ all samples are equal

Fixes golang/go#82128

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[gopherbot]

Message from Jean-Baptiste Lernout:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Ville Vesilehto:

Patch Set 1:

(1 comment)

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