Remove parity-wasm dependency from contract-build crate

[smiasojed]

Summary

Closes #1141

• y/n | Does it introduce breaking changes?
• y/n | Is it dependent on the specific version of ink or pallet-contracts?

Replace parity-wasm usage for post processing with wasmparser and wasm-encoder

Description

Remove parity-wasm from contract-build crate
Implement the WASM post-processing logic with wasmparser and wasm-encoder crates

Checklist before requesting a review

• My code follows the style guidelines of this project
• I have added an entry to CHANGELOG.md
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules

[ascjones]

Have you tested this against some standard contracts to check that the sizes are the same (or better!)? Would be good to run the contract size check against the integration-tests.

Also I'd like to see this wasm post-processing refactored to a separate module, this lib.rs file is big enough already!

[ascjones]

Maybe post_process_module could return an allocated Vec<u8> since it looks like every usage just passes a new buffer instance.

[smiasojed]

Have you tested this against some standard contracts to check that the sizes are the same (or better!)?
I tested it on some ink-examples, and the output was the same for both the old and new implementations.