Add bool flag to validation for EVM context

[sieniven]

Summary

• execTestTx implementation uses the validation pipeline, which creates undesirable behavior when testing evm tx execution. Specifically, the function is called in eth RPC and dvm RPC.
• Fix to pass a boolean flag to the visitor pattern in validation (mn_checks) where we will pass that flag on to evm_try_prevalidate_raw_tx to validate the raw evm tx with or without evm context.
• Note that evmContext = 0 is safe as it is double guarded in txqueue to be an invalid context key.

Implications

• Storage

  • Database reindex required
  • Database reindex optional
  • Database reindex not required
  • None

• Consensus

  • Network upgrade required
  • Includes backward compatible changes
  • Includes consensus workarounds
  • Includes consensus refactors
  • None