Update reaction fingerprints to use generators

[vfscalfani]

This is a follow up of discussion #7489. It affects all versions of RDKit.

Is your feature request related to a problem? Please describe.

The current implementation of reaction fingerprints does not yet use the new fingerprint generator method.

Describe the solution you'd like

Update the reaction fingerprint code to use generators.

Describe alternatives you've considered

Current code works fine, but produces a deprecation warning.

Additional context

Thanks