This is a preparation step for allowing subscripting containers to
transform only a prefix of an indirection list and modify the list
in-place by removing the processed elements. Currently, all elements
are consumed, and the list is set to NIL after transformation.

In the following commit, subscripting containers will gain the
flexibility to stop transformation when encountering an unsupported
indirection and return the remaining indirections to the caller.

This change extends generic type subscripting to recognize dot
notation (.) in addition to bracket notation ([]). While this does not
yet provide full support for dot notation, it enables subscripting
containers to process it in the future.

For now, container-specific transform functions only handle
subscripting indices and stop processing when encountering dot
notation. It is up to individual containers to decide how to transform
dot notation in subsequent updates.

This is a preparation step for a future commit that will reuse the
aforementioned function.

This is a preparation step for a future commit that will reuse the
aforementioned function.

Now that we are allowing container generic subscripting to take dot
notation in the list of indirections, and it is transformed as a
String node.

For jsonb, we want to represent field accessors as String nodes in
refupperexprs for distinguishing from ordinary text subscripts which
can be needed for correct EXPLAIN.

Strings node is no longer a valid expression nodes, so added special
handling for them in walkers in nodeFuncs etc.

This patch introduces JSONB member access using dot notation, wildcard
access, and array subscripting with slicing, aligning with the JSON
simplified accessor specified in SQL:2023. Specifically, the following
syntax enhancements are added:

1. Simple dot-notation access to JSONB object fields
2. Wildcard dot-notation access to JSONB object fields
2. Subscripting for index range access to JSONB array elements

Examples:

-- Setup
create table t(x int, y jsonb);
insert into t select 1, '{"a": 1, "b": 42}'::jsonb;
insert into t select 1, '{"a": 2, "b": {"c": 42}}'::jsonb;
insert into t select 1, '{"a": 3, "b": {"c": "42"}, "d":[11, 12]}'::jsonb;

-- Existing syntax predates the SQL standard:
select (t.y)->'b' from t;
select (t.y)->'b'->'c' from t;
select (t.y)->'d'->0 from t;

-- JSON simplified accessor specified by the SQL standard:
select (t.y).b from t;
select (t.y).b.c from t;
select (t.y).d[0] from t;

The SQL standard states that simplified access is equivalent to:
JSON_QUERY (VEP, 'lax $.JC' WITH CONDITIONAL ARRAY WRAPPER NULL ON EMPTY NULL ON ERROR)

where:
  VEP = <value expression primary>
  JC = <JSON simplified accessor op chain>

For example, the JSON_QUERY equivalents of the above queries are:

select json_query(y, 'lax $.b' WITH CONDITIONAL ARRAY WRAPPER NULL ON EMPTY NULL ON ERROR) from t;
select json_query(y, 'lax $.b.c' WITH CONDITIONAL ARRAY WRAPPER NULL ON EMPTY NULL ON ERROR) from t;
select json_query(y, 'lax $.d[0]' WITH CONDITIONAL ARRAY WRAPPER NULL ON EMPTY NULL ON ERROR) from t;

Implementation details:

Extends the existing container subscripting interface to support
container-specific information, specifically a JSONPath expression for
jsonb.

During query transformation, detects dot-notation, wildcard access,
and sliced subscripting. If any of these accessors are present,
constructs a JSONPath expression representing the access chain.

During execution, if a JSONPath expression is present in
JsonbSubWorkspace, executes it via JsonPathQuery().

Does not transform accessors directly into JSON_QUERY during
transformation to preserve the original query structure for EXPLAIN
and CREATE VIEW.