BadVoucherRequestHandler can´t extends because isn´t export in the pubic_api

[Alejo-Fonseca-Pyxis]

Describe the bug
With the newest Version 6.6.0 of spartacus, the request handlers for Cart and Voucher cannot be extended, as the seem to not be correctly exported / exposed.

Tell us the version of Spartacus

Library version: 6.6.0
To Reproduce
Steps to reproduce the behavior:

Create new Spartacus 6.6.0 project
Create your own BadVoucherRequestHandler which extends the spartacus default class
Notice the console build error
Expected behaviour
It is possible to extend these request handlers with a custom class

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