Support referrent-explicit format creating presentation request

[Patrik-Stas]

• When creating proof request, our API expected list of <predicate_info> objects (as they are defined in https://hyperledger.github.io/anoncreds-spec/#create-presentation-request). Aries-vcx implementation then auto-generated referent names, eg given:

[
  { name: 'age', p_type: '>=', p_value: 18 }, 
  { name: 'balance', p_type: '>=', p_value: 10000 }
]

we transformed the input internally to anoncreds format

{
  predicate_0: { name: 'age', p_type: '>=', p_value: 18 }, 
  predicate_1: { name: 'balance', p_type: '>=', p_value: 10000 }
}

• This PR enabled API called to simply supply entire requested_predicates object (as per anoncreds link above) and therefore letting the caller specify referents names eg.

{
  is_adult: { name: 'age', p_type: '>=', p_value: 18 }, 
  credit: { name: 'balance', p_type: '>=', p_value: 10000 }
}

This is useful capability when inspecting presentations.

Note

• We should remove vector format, it's convenient but not very useful
• String parsing should be happening on layer above aries-vcx
• But these are for different PRs

[codecov-commenter]

Codecov Report

Merging #844 (58d01a8) into main (f1314ef) will decrease coverage by 40.30%.
The diff coverage is 36.00%.

@@            Coverage Diff             @@
##             main    #844       +/-   ##
==========================================
- Coverage   49.00%   8.70%   -40.30%     
==========================================
  Files         414     408        -6     
  Lines       33694   32864      -830     
  Branches     7446    7200      -246     
==========================================
- Hits        16512    2862    -13650     
- Misses      12066   29191    +17125     
+ Partials     5116     811     -4305     

Flag	Coverage Δ
unittests-aries-vcx	8.70% <36.00%> (-40.27%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aries_vcx/src/common/proofs/proof_request.rs	60.35% <36.00%> (-1.91%)	⬇️

... and 304 files with indirect coverage changes

[gmulhearn]

had a passing browse of this; Rust changes LGTM! Keen for the typing changes in #845 . inspired me to make this ticket #847

[bobozaur]

Left some comments about readability mainly.

[bobozaur]

Had a short discussion with @Patrik-Stas who pointed out this is kind of legacy code and will most likely get refactored soon.

Since previous comments were mainly about readability, I have no problem with merging this as-is now.