Remove WQL & define proof request restrictions format

[TimoGlastra]

See #118 for extra context.

This issue focusses on a) the removal of WQL from the AnonCreds specification, and b) defining the allowed fields in the restrictions field of a proof request.

I think for backwards compatibility we should keep the fields ending in _did and only allow them for the legacy indy identifier use case. Other should use the _id variant.

The question is how far we want to go in supporting restrictions in the proof request. I think most aries implementations have only implemented the following:

• schema_id
• cred_def_id
• schema_issuer_did
• schema_name
• schema_version
• issuer_did
• rev_reg_id
• attribute value query (attr:<atttr_name>:value -> <value>)

The current AnonCreds spec has a whole sections on WQL and suggests we can also use:

• $like for fuzzy search
• $gt, $lt, $gte, $lte for size comparison
• $in for matching that a value is in a set
• attribute existence query (attr::<attribute name>::marker -> 1)

Implementing the above as well means it will be more like a competitor to the Presentation Exchange protocol that allows advanced filtering.

Either way, I think we shouldn't call it Wallet Query Language, but rather call it something specific to proof request restrictions.

Some other notes:

• There's currently a mention of ~ for unencrypted tags. As that is more of an implementation detail we can remove this part completely

[swcurran]

I'm working on the Presentation Request section (PR today? probably...) and will remove the WQL there, and agree it needs to be removed from the rest. I don't think rev_reg_id is supported, is it? And even if it is, who cares? :-) I think that the existence of an attribute might be supported.

My plan is to work through the rest of the presentation docs as well.

[swcurran]

Per discussion at AnonCreds spec. meeting 2023.01.09 -- closing, addressed by #128