Smart Contracts: execute_condition & execute_function return structs

[bchamagne]

Description

Every functions that executes a contract now returns a struct.
This allow for the playground to display the errors from condition/public function.

It also prepare the ground for the logs and for the validation errors (in 2 next PRs)

Type of change

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Tested with the playground (branch: develop)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Neylix]

LGTM
Tested with dex, it works as expected (just need to rebase develop to take last commits that solved some encoding bugs)