Being more straightforward on variables vs identifiers in the AST

[vgapeyev]

This is the 3rd preliminary PR towards #1122, on top of PR #1178 and PR #1187.

The AST node for a variable reference, Expr.Vr (formerly Expr.Id) now has an identifier (Id, formerly Identifier) as its field, instead of repeating the latter's fields.
There have been some comments in partiql.ion (now removed) alluding to the awkwardness of the prior situation.

There is also some renaming, for better mnemonics.

The primary change for the above is in partiql.ion and can be summarized as this:

(id                               -->          (vr
   name::symbol                   -->               id::id
   case::case_sensitivity         -->
   qualifier::scope_qualifier)                      qualifier::scope_qualifier)

(product identifier               -->          (product id
   name::symbol                   -->                symb::symbol
   case::case_sensitivity)                           case::case_sensitivity)

(product defnid symb::symbol)                  (product defnid symb::symbol)

The rest is the mechanical churn necessary to make it work.

As a reminder, the former id is a variant of the expr union, which was used for variable references. The new name vr better reflects this role. This renaming has freed id for the "bare" identifiers. (The shorter name is handy, as vr and id are used in many-many tests.)

• Updated Unreleased Section in CHANGELOG: [YES]
• Any backward-incompatible changes? [YES]
• Any new external dependencies? [NO]
• Do your changes comply with the Contributing Guidelines
  and Code Style Guidelines? [YES]

License Information

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[github-actions]

Conformance comparison report

	Base (1ece3aa)	cd12122	+/-
% Passing	92.40%	92.40%	0.00%
✅ Passing	5376	5376	0
❌ Failing	442	442	0
🔶 Ignored	0	0	0
Total Tests	5818	5818	0

Number passing in both: 5376

Number failing in both: 442

Number passing in Base (1ece3aa) but now fail: 0

Number failing in Base (1ece3aa) but now pass: 0

[codecov-commenter]

Codecov Report

Patch coverage: 86.60% and project coverage change: -0.01% ⚠️

Comparison is base (1ece3aa) 72.84% compared to head (3d28210) 72.84%.

Additional details and impacted files

@@                Coverage Diff                 @@
##             sqlid-defnid    #1194      +/-   ##
==================================================
- Coverage           72.84%   72.84%   -0.01%     
  Complexity           2352     2352              
==================================================
  Files                 221      221              
  Lines               16847    16846       -1     
  Branches             3147     3147              
==================================================
- Hits                12272    12271       -1     
  Misses               3600     3600              
  Partials              975      975              

Flag	Coverage Δ
CLI	14.28% <ø> (ø)
EXAMPLES	80.28% <ø> (ø)
LANG	78.86% <86.60%> (-0.01%)	⬇️

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

Files Changed	Coverage Δ
...tiql/examples/PartialEvaluationVisitorTransform.kt	92.30% <ø> (ø)
...iql-lang/src/main/kotlin/org/partiql/lang/Ident.kt	68.75% <ø> (ø)
...artiql/lang/eval/physical/operators/Accumulator.kt	85.00% <0.00%> (ø)
...tlin/org/partiql/lang/prettyprint/RecursionTree.kt	100.00% <ø> (ø)
...c/main/kotlin/org/partiql/lang/CompilerPipeline.kt	93.75% <50.00%> (ø)
...org/partiql/lang/prettyprint/QueryPrettyPrinter.kt	78.29% <50.00%> (ø)
.../visitors/GroupByPathExpressionVisitorTransform.kt	80.76% <60.00%> (-0.25%)	⬇️
...rtiql/lang/planner/transforms/plan/RelConverter.kt	66.82% <66.66%> (-0.16%)	⬇️
...sforms/LogicalToLogicalResolvedVisitorTransform.kt	93.62% <75.00%> (ø)
...planner/transforms/AstToLogicalVisitorTransform.kt	86.20% <90.00%> (-0.08%)	⬇️
... and 14 more

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