ValidateSmartContractCall better conflict resolution

[bchamagne]

Description

Take into account the latest_validation_time when resolving conflicts on contract calls execution.
I based this PR on #1343. Please ignore all commits but last 3.
Fixes #1485

Type of change

• Enhancement

How Has This Been Tested?

unit-tested

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