[Execution Node] Reduce size and growth rate of mtrie by merging 5 kinds of FVM account payloads to reduce payloads per account

[fxamacker]

Problem

About 5 FVM account payloads are created for every account which can cause mtrie to grow quickly when large number of accounts are created.

Proposed Solution

Merge 5 kinds of FVM account payloads to reduce the number of payloads per account.

• exists
• storage_used
• storage_index
• frozen
• public_key_count

Updates #1744
Updates #2502 (This PR merges exists and frozen payloads among other improvements)

Thanks @ramtinms for making time to sync about this on Friday and confirming approach! 👍

Misc

Breakdown of FVM account payloads:

• Every account has 3 FVM account payloads: exists, storage_used, storage_index.
• ~99% accounts have public_key_count payload, and each public key is stored in a separate payload under the key of public_key_ + index.
• Some accounts have contract_names payload, and each contract is stored in a separate payload under the key of code. + contract name.
• Frozen account has frozen payload.