Add option to clear the rules token if it can't be replaced

Problem/Motivation

It's currently not possible to clear tokens if they're unused because it uses the default option which is to have it disabled.

Steps to reproduce

Provide a rules token with an irreplaceable token.

Proposed resolution

Provide a global setting, with the option to have granular options that can be set on the individual context data level - see 🌱 [meta] Data Processors Active

Remaining tasks

Provide issue fork.

User interface changes

There's a global setting to enable clearing of invalid tokens.

As well as the ability to set individual context processor settings, e.g. if only a specific field needs to clear the token or opt out.

API changes

Introduce new interfaces and classes for context data processor plugins that can provide form configurations.

Data model changes

N/A