Add initial contract macro benchmarks

[athei]

In addition to the extensive synthetic benchmark suite we have in contracts that is used to determine weights we want to add a set of benchmarks that use real world benchmarks. That will give us a tool to compare the progress of different contract languages (ink, solang) and execution engines (wasmi, wasmer).

This PR creates some infrastructure code to allow that benchmarks to be written and adds the first two benchmarks:

• erc20 transfer using the ink! erc20 example contract
• erc20 transfer using the openzeppelin erc20 contract compiled with solang

You can run those benchmarks by running this commandline in the substrate repo:

cargo run --release --features runtime-benchmarks,[wasmer-sandbox] -- --extra --dev --execution=wasm --wasm-execution=compiled -p pallet_contracts -e ink_erc20_transfer

The wasmer-sandbox feature is optional and can be used to run the benchmark using wasmer. I ran both benchmarks using wasmi and wasmer. The g parameter describes whether gas instrumentation is injected or not. These are the results from running it on a rather slow x64 linux:

ink_erc20_transfer, wasmi

Min Squares Analysis
========
-- Extrinsic Time --

Data points distribution:
    g   mean µs  sigma µs       %
    0      5949     21.06    0.3%
    1      8795     53.03    0.6%

Quality and confidence:
param     error
g         8.151

Model:
Time ~=     5949
    + g     2845
              µs


ink_erc20_transfer, wasmer

Min Squares Analysis
========
-- Extrinsic Time --

Data points distribution:
    g   mean µs  sigma µs       %
    0      6010     11.97    0.1%
    1      9453     15.15    0.1%

Quality and confidence:
param     error
g         2.759

Model:
Time ~=     6010
    + g     3442
              µs



solang_erc20_transfer, wasmi

Min Squares Analysis
========
-- Extrinsic Time --

Data points distribution:
    g   mean µs  sigma µs       %
    0      2050     9.492    0.4%
    1      2179     13.77    0.6%

Quality and confidence:
param     error
g         2.389

Model:
Time ~=     2050
    + g    128.9
              µs


solang_erc20_transfer, wasmer

Min Squares Analysis
========
-- Extrinsic Time --

Data points distribution:
    g   mean µs  sigma µs       %
    0      2046     9.061    0.4%
    1      2134     5.513    0.2%

Quality and confidence:
param     error
g         1.515

Model:
Time ~=     2046
    + g    88.56
              µs

[cmichi]

LGTM!

[athei]

bot merge

[ghost]

Trying merge.