[19.0][ADD] account_payment_internal_transfer

[alan196]

Port to 19.0 of OCA#923, which restores the internal transfer functionality removed from the account module in Odoo 18.0.

Same content as the upstream PR OCA#959, opened so it is available in the Jarsa fork while the OCA review is in progress.

• Internal Transfer checkbox + Destination Journal on payments.
• Automatic paired payment in the destination journal using the company transfer account, with automatic reconciliation.
• Cascade of cancel/draft/unlink between paired payments.
• Internal Transfer shortcut in the bank/cash journal dashboard.

All 10 unit tests pass on a clean 19.0 database.

[jarsabot]

    **WARNING**: Could not link to Odoo task. Record ID not found in the title of the MR, supported formats:

{ record type }#{ number }

Available types: 'task#', 't#' (case insensitive)

Examples:

• task#123

• i#123