Add benchmarks for wasmi builtin metering (paritytech#56)

* Upgraded to newest wasmi
* Refactored benchmarks
* Two new benchmark strategies (`no_metering` and `wasmi_builtin`)

We can now benchmark the execution of modules using our two
instrumentation strategies in addition to no metering (as a baseline)
and wasmi's builtin metering.

We can learn from the following results (ran on my M1) that the builtin
metering decisively outperforms the instrumentation on every single
fixture.

cc @Robbepop 

```
coremark/no_metering                    [15.586 s 15.588 s 15.589 s]
coremark/wasmi_builtin                  [16.403 s 16.414 s 16.434 s]
coremark/host_function                  [18.245 s 18.248 s 18.252 s]
coremark/mutable_global                 [20.476 s 20.486 s 20.505 s]

recursive_ok/no_metering                [111.32 µs 111.33 µs 111.34 µs]
recursive_ok/wasmi_builtin              [138.64 µs 138.65 µs 138.66 µs]
recursive_ok/host_function              [495.55 µs 495.64 µs 495.78 µs]
recursive_ok/mutable_global             [514.07 µs 514.09 µs 514.11 µs]

fibonacci_recursive/no_metering         [3.9098 µs 3.9102 µs 3.9108 µs]
fibonacci_recursive/wasmi_builtin       [4.3242 µs 4.3246 µs 4.3250 µs]
fibonacci_recursive/host_function       [12.913 µs 12.914 µs 12.915 µs]
fibonacci_recursive/mutable_global      [13.202 µs 13.208 µs 13.212 µs]
              
factorial_recursive/no_metering         [530.72 ns 530.84 ns 530.91 ns]
factorial_recursive/wasmi_builtin       [619.17 ns 619.30 ns 619.44 ns]
factorial_recursive/host_function       [1.7656 µs 1.7657 µs 1.7659 µs]
factorial_recursive/mutable_global      [1.8783 µs 1.8786 µs 1.8788 µs]

count_until/no_metering                 [1.2422 ms 1.2423 ms 1.2424 ms]
count_until/wasmi_builtin               [1.3976 ms 1.3978 ms 1.3981 ms]
count_until/host_function               [4.8074 ms 4.8106 ms 4.8125 ms]
count_until/mutable_global              [5.9161 ms 5.9169 ms 5.9182 ms]

memory_vec_add/no_metering              [4.1630 ms 4.1638 ms 4.1648 ms]
memory_vec_add/wasmi_builtin            [4.3913 ms 4.3925 ms 4.3930 ms]
memory_vec_add/host_function            [8.2925 ms 8.2949 ms 8.2967 ms]
memory_vec_add/mutable_global           [9.1124 ms 9.1152 ms 9.1163 ms]

wasm_kernel::tiny_keccak/no_metering    [613.21 µs 613.42 µs 613.58 µs]
wasm_kernel::tiny_keccak/wasmi_builtin  [617.04 µs 617.46 µs 617.81 µs]
wasm_kernel::tiny_keccak/host_function  [817.24 µs 817.44 µs 817.89 µs]
wasm_kernel::tiny_keccak/mutable_global [873.42 µs 873.90 µs 874.65 µs]

global_bump/no_metering                 [1.4597 ms 1.4598 ms 1.4600 ms]
global_bump/wasmi_builtin               [1.6151 ms 1.6152 ms 1.6153 ms]
global_bump/host_function               [5.5393 ms 5.5418 ms 5.5435 ms]
global_bump/mutable_global              [6.9446 ms 6.9454 ms 6.9461 ms]
```

Cargo.toml

@@ -12,9 +12,14 @@ repository = "https://github.com/paritytech/wasm-instrument"
 include = ["src/**/*", "LICENSE-*", "README.md"]
 
 [[bench]]
-name = "benches"
+name = "instrumentation"
 harness = false
-path = "benches/benches.rs"
+path = "benches/instrumentation.rs"
+
+[[bench]]
+name = "execution"
+harness = false
+path = "benches/execution.rs"
 
 [profile.bench]
 lto = "fat"
@@ -32,7 +37,7 @@ rand = "0.8"
 wat = "1"
 wasmparser = "0.101"
 wasmprinter = "0.2"
-wasmi = "0.22"
+wasmi = "0.28"
 
 [features]
 default = ["std"]