Export the participant list, in order at the front of the mermaid output

[jandrieu]

for example
sequenceDiagram
              autonumber
    participant Browser
    participant C-Store Website          
    participant Nelson (Customer)
    participant TruAge
    participant POS
    C-Store Website->>C-Store Website:Process payment
    C-Store Website->>Browser:Payment complete, digital receipt
    Browser->>Nelson (Customer):Display payment complete, prompt for digital receipt
    C-Store Website->>TruAge:Final shopping cart update
    TruAge->>TruAge:Finalize current transaction
    Nelson (Customer)->>Nelson (Customer):Decide to save receipt
    TruAge->>TruAge:Update analytics servers
    Nelson (Customer)->>Browser:Store the receipt
    C-Store Website->>POS:Payment received
    Browser->>Nelson (Customer):Display wallet selector
    TruAge->>C-Store Website:Status update
    Nelson (Customer)->>Browser:Wallet selection
    POS->>Bill (Clerk):Payment received
    Browser->>Digital Wallet:Store receipt
    Digital Wallet->>Digital Wallet:Store receipt
    Digital Wallet->>Browser:Receipt successfully stored
    Bill (Clerk)->>POS:Status update
    Browser->>Nelson (Customer):Receipt successfully stored
    POS->>C-Store Website:Status update
    Bill (Clerk)->>Bill (Clerk):Finish bagging

sequenceDiagram
             autonumber
   participant Browser
   participant C-Store Website          
   participant Nelson (Customer)
   participant TruAge
   participant POS
   C-Store Website->>C-Store Website:Process payment
   C-Store Website->>Browser:Payment complete, digital receipt
   Browser->>Nelson (Customer):Display payment complete, prompt for digital receipt
   C-Store Website->>TruAge:Final shopping cart update
   TruAge->>TruAge:Finalize current transaction
   Nelson (Customer)->>Nelson (Customer):Decide to save receipt
   TruAge->>TruAge:Update analytics servers
   Nelson (Customer)->>Browser:Store the receipt
   C-Store Website->>POS:Payment received
   Browser->>Nelson (Customer):Display wallet selector
   TruAge->>C-Store Website:Status update
   Nelson (Customer)->>Browser:Wallet selection
   POS->>Bill (Clerk):Payment received
   Browser->>Digital Wallet:Store receipt
   Digital Wallet->>Digital Wallet:Store receipt
   Digital Wallet->>Browser:Receipt successfully stored
   Bill (Clerk)->>POS:Status update
   Browser->>Nelson (Customer):Receipt successfully stored
   POS->>C-Store Website:Status update
   Bill (Clerk)->>Bill (Clerk):Finish bagging

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