[19.0][ADD] purchase_partner_display_ref

[JasminSForgeFlow]

This module prefixes the supplier reference (res.partner.supplier_ref) to the
vendor's display_name whenever it is rendered inside a Purchase view —
typically as [V00045] Acme Supplies in the autocomplete dropdown of the vendor
field on a purchase order.

The decoration mechanism lives in the generic partner_display_ref module; this
module injects the partner_display_ref_field context key (set to
supplier_ref) into the Purchase views and registers supplier_ref as a
dependency of the vendor display_name. Other views that read display_name
continue to see the plain partner name.

Depends on:

• [19.0][ADD] partner_display_ref partner-contact#2384

@ForgeFlow

[BhaveshHeliconia]

LGTM!