cmd/compile: implement Avg64u, Hmul64, Hmul64u for wasm

cmd/compile: implement Avg64u, Hmul64, Hmul64u for wasm

This lets us remove useAvg and useHmul from the division rules.
The compiler is simpler and the generated code is faster.

goos: wasip1
goarch: wasm
pkg: internal/strconv
                               │   old.txt   │               new.txt               │
                               │   sec/op    │   sec/op     vs base                │
AppendFloat/Decimal              192.8n ± 1%   194.6n ± 0%   +0.91% (p=0.000 n=10)
AppendFloat/Float                328.6n ± 0%   279.6n ± 0%  -14.93% (p=0.000 n=10)
AppendFloat/Exp                  335.6n ± 1%   289.2n ± 1%  -13.80% (p=0.000 n=10)
AppendFloat/NegExp               336.0n ± 0%   289.1n ± 1%  -13.97% (p=0.000 n=10)
AppendFloat/LongExp              332.4n ± 0%   285.2n ± 1%  -14.20% (p=0.000 n=10)
AppendFloat/Big                  348.2n ± 0%   300.1n ± 0%  -13.83% (p=0.000 n=10)
AppendFloat/BinaryExp            137.4n ± 0%   138.2n ± 0%   +0.55% (p=0.001 n=10)
AppendFloat/32Integer            193.3n ± 1%   196.5n ± 0%   +1.66% (p=0.000 n=10)
AppendFloat/32ExactFraction      283.3n ± 0%   268.9n ± 1%   -5.08% (p=0.000 n=10)
AppendFloat/32Point              279.9n ± 0%   266.5n ± 0%   -4.80% (p=0.000 n=10)
AppendFloat/32Exp                300.1n ± 0%   288.3n ± 1%   -3.90% (p=0.000 n=10)
AppendFloat/32NegExp             288.2n ± 1%   277.9n ± 1%   -3.59% (p=0.000 n=10)
AppendFloat/32Shortest           261.7n ± 0%   250.2n ± 0%   -4.39% (p=0.000 n=10)
AppendFloat/32Fixed8Hard         173.3n ± 1%   158.9n ± 1%   -8.31% (p=0.000 n=10)
AppendFloat/32Fixed9Hard         180.0n ± 0%   167.9n ± 2%   -6.70% (p=0.000 n=10)
AppendFloat/64Fixed1             167.1n ± 0%   149.6n ± 1%  -10.50% (p=0.000 n=10)
AppendFloat/64Fixed2             162.4n ± 1%   146.5n ± 0%   -9.73% (p=0.000 n=10)
AppendFloat/64Fixed2.5           165.5n ± 0%   149.4n ± 1%   -9.70% (p=0.000 n=10)
AppendFloat/64Fixed3             166.4n ± 1%   150.2n ± 0%   -9.74% (p=0.000 n=10)
AppendFloat/64Fixed4             163.7n ± 0%   149.6n ± 1%   -8.62% (p=0.000 n=10)
AppendFloat/64Fixed5Hard         182.8n ± 1%   167.1n ± 1%   -8.61% (p=0.000 n=10)
AppendFloat/64Fixed12            222.2n ± 0%   208.8n ± 0%   -6.05% (p=0.000 n=10)
AppendFloat/64Fixed16            197.6n ± 1%   181.7n ± 0%   -8.02% (p=0.000 n=10)
AppendFloat/64Fixed12Hard        194.5n ± 0%   181.0n ± 0%   -6.99% (p=0.000 n=10)
AppendFloat/64Fixed17Hard        205.1n ± 1%   191.9n ± 0%   -6.44% (p=0.000 n=10)
AppendFloat/64Fixed18Hard        6.269µ ± 0%   6.643µ ± 0%   +5.97% (p=0.000 n=10)
AppendFloat/64FixedF1            211.7n ± 1%   197.0n ± 0%   -6.95% (p=0.000 n=10)
AppendFloat/64FixedF2            189.4n ± 0%   174.2n ± 0%   -8.08% (p=0.000 n=10)
AppendFloat/64FixedF3            169.0n ± 0%   154.9n ± 0%   -8.32% (p=0.000 n=10)
AppendFloat/Slowpath64           321.2n ± 0%   274.2n ± 1%  -14.63% (p=0.000 n=10)
AppendFloat/SlowpathDenormal64   307.4n ± 1%   261.2n ± 0%  -15.03% (p=0.000 n=10)
AppendInt                        3.367µ ± 1%   3.376µ ± 0%        ~ (p=0.517 n=10)
AppendUint                       675.5n ± 0%   676.9n ± 0%        ~ (p=0.196 n=10)
AppendIntSmall                   28.13n ± 1%   28.17n ± 0%   +0.14% (p=0.015 n=10)
AppendUintVarlen/digits=1        20.70n ± 0%   20.51n ± 1%   -0.89% (p=0.018 n=10)
AppendUintVarlen/digits=2        20.43n ± 0%   20.27n ± 0%   -0.81% (p=0.001 n=10)
AppendUintVarlen/digits=3        38.48n ± 0%   37.93n ± 0%   -1.43% (p=0.000 n=10)
AppendUintVarlen/digits=4        41.10n ± 0%   38.78n ± 1%   -5.62% (p=0.000 n=10)
AppendUintVarlen/digits=5        42.25n ± 1%   42.11n ± 0%   -0.32% (p=0.041 n=10)
AppendUintVarlen/digits=6        45.40n ± 1%   43.14n ± 0%   -4.98% (p=0.000 n=10)
AppendUintVarlen/digits=7        46.81n ± 1%   46.03n ± 0%   -1.66% (p=0.000 n=10)
AppendUintVarlen/digits=8        48.88n ± 1%   46.59n ± 1%   -4.68% (p=0.000 n=10)
AppendUintVarlen/digits=9        49.94n ± 2%   49.41n ± 1%   -1.06% (p=0.000 n=10)
AppendUintVarlen/digits=10       57.28n ± 1%   56.92n ± 1%   -0.62% (p=0.045 n=10)
AppendUintVarlen/digits=11       60.09n ± 1%   58.11n ± 2%   -3.30% (p=0.000 n=10)
AppendUintVarlen/digits=12       62.22n ± 0%   61.85n ± 0%   -0.59% (p=0.000 n=10)
AppendUintVarlen/digits=13       64.94n ± 0%   62.92n ± 0%   -3.10% (p=0.000 n=10)
AppendUintVarlen/digits=14       65.42n ± 1%   65.19n ± 1%   -0.34% (p=0.005 n=10)
AppendUintVarlen/digits=15       68.17n ± 0%   66.13n ± 0%   -2.99% (p=0.000 n=10)
AppendUintVarlen/digits=16       70.21n ± 1%   70.09n ± 1%        ~ (p=0.517 n=10)
AppendUintVarlen/digits=17       72.93n ± 0%   70.49n ± 0%   -3.34% (p=0.000 n=10)
AppendUintVarlen/digits=18       73.01n ± 0%   72.75n ± 0%   -0.35% (p=0.000 n=10)
AppendUintVarlen/digits=19       79.27n ± 1%   79.49n ± 1%        ~ (p=0.671 n=10)
AppendUintVarlen/digits=20       82.18n ± 0%   80.43n ± 1%   -2.14% (p=0.000 n=10)
geomean                          143.4n        136.0n        -5.20%

Change-Id: I8245814a0259ad13cf9225f57db8e9fe3d2e4267
Reviewed-on: https://go-review.googlesource.com/c/go/+/717407
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>