Define PlutusV4 script context

[lehins]

This ticket is created to track progress on PlutusV4 context that will include at least two CIPs:

• CIP-112 - Observe script type
• CIP-118 - Nested Transactions

Considering that CIP-112 will be required for CIP-118 it makes sense to start with it first.

• - Define PlutusV4 version in plutus-ledger-api:

  plutus/plutus-ledger-api/src/PlutusLedgerApi/Common/Versions.hs

  Lines 89 to 92 in fa5c9e6

  	data PlutusLedgerLanguage =
  	PlutusV1 -- ^ introduced in Alonzo HF
  	| PlutusV2 -- ^ introduced in Vasil HF
  	| PlutusV3 -- ^ introduced in Chang HF

• - Create V4 in plutus-ledger-api:PlutusLedgerApi that reuses as much stuff from V1-V3 as possible
• - Define TxInfo for PlutusV4
• - Add txInfoGuards :: [Credential] to TxInfo for PlutusV4 field and remove txInfoSignatories, since former supersedes the latter (Note that we will be using the term Guards in the implementation instead of Observers as CIP-112. CC @colll78 if you are still up to renaming the CIP to avoid confusion)
• - Add Guarding script purpose
• - Remove PointerAddress case for PlutusV4. See Fail PlutusV4 TxInfo translation when a Ptr is present in any of the outputs cardano-ledger#4832 for reference
• - TBD: CIP-118 related parts added to TxInfo.

I'd recommend creating a child ticket for each of the bullet points, so the progress can be tracked at more granular level, but I'll leave this up to the Plutus team.

[zliu41]

Two specific things to note

1. We'll add two new constructors to Data - Array and Value, and they will be used in Plutus V4 script context. The script context for V1-V3 will of course remain the same.
2. We are not yet sure whether we can implement https://cips.cardano.org/cip/CIP-0152 in time for Dijkstra. If we can, then that will also impact the script context.

[colll78]

I think a clear non-controversial change is to add a ownScriptHash field to the ScriptContext.

-- | The context that the currently-executing script can access.
data ScriptContext = ScriptContext
  { scriptContextTxInfo     :: TxInfo
  -- ^ information about the transaction the currently-executing script is included in
  , scriptContextRedeemer   :: V2.Redeemer
  -- ^ Redeemer for the currently-executing script
  , scriptContextScriptInfo :: ScriptInfo
  -- ^ the purpose of the currently-executing script, along with information associated
  -- with the purpose
  , scriptContextOwnScriptHash :: ScriptHash 
  -- ^ the hash of the currently-executing script. 
  }