[MOV] crm: move lead to opportunity in mass wizard in its own files

Lead 2 opportunity wizard file actually holds 2 wizards. Let us split files
especially that naming is quite obfuscated.

LINKS

Side effect of Task ID 2056759 (remove crm.partner.binding mixin)
Side effect of Task ID 2088565 (crm onchange -> compute)
Community PR #43127
Enterprise PR odoo/enterprise#7656