Fix: Update solidity of transactions from past to present in TransactionValidator

[luca-moser]

Description

Changes the TransactionValidator's checkSolidity() method to use a LinkedHashSet in order to keep the order in which transactions got analyzed. The TransactionViewModel'supdateSolidTransactions() method will then update the solid flag of the given txs in reverse order to guarantee that the flags are updated from past to present.

refs: #1491

Fixes # (issue)
#1187 (maybe)
#1292 (maybe)

Type of change

• Bug fix (a non-breaking change which fixes an issue)

How Has This Been Tested?

Private Net.

Checklist:

• My code follows the style guidelines for 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
• 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