Procedures: add WASM ABI for anonymous mutable transactions

[Centril]

Description of Changes

Unstably adds the ABIs:

pub fn procedure_start_mut_transaction() -> u16;
pub fn procedure_commit_mut_transaction() -> u16;
pub fn procedure_abort_mut_transaction() -> u16;

API and ABI breaking changes

None

Expected complexity level and risk

2 -- pretty localized stuff.

Testing

This is just the wasm syscall ABI. Once bindings is added atop of this, tests will be included too.