Support more types of parameters to JSON path

[kasiafi]

Before this change, path parameters could be only: numeric, boolean, datetime
and string values, and other values that could be implicitly coerced to varchar.

After this change, any values are accepted which can be coerced
to varchar. It is no more required that an implicit coercion is defined.

# General
* Support all types that can be cast to `varchar` as parameters to JSON path.

[martint]

For completeness, this is per section 10.12.3 - JSON value expression of the SQL specification:

3. The declared type DT of the <value expression> VE simply contained in <JSON value expression> JVE either shall be a character string type, a binary string type, a numeric type, a datetime type, or Boolean, or shall be a <data type> the values of which can be cast to a character string type according to the Syntax Rules of Subclause 6.13, “`”.

[martint]

Why do we need to track these explicitly? It should be sufficient to just register a coercion via addOrReplaceExpressionsCoercion.

[kasiafi]

I considered that approach, but so far that mechanism was only used for implicit coercions. I didn't want to mix in the JSON path parameter coercions, which are part of JSON functions semantics rather than SQL type alignment.

[martint]

That mechanism is for anything where the analyzer decides a cast needs to be inserted, so it should be safe to use here. The concept of whether an implicit coercion is allowed is an analysis time concern and the planner doesn't care about why a cast needs to be inserted.

[martint]

In fact, we could say that this is an implicit coercion, just in a very narrow scope (json function parameters)

[kasiafi]

I switched to the existing mechanism (addOrReplaceExpressionsCoercion).

[kasiafi]

For completeness, this is per section 10.12.3 - JSON value expression of the SQL specification

Yes, that was the intention behind the code from the start. I just chose the wrong check: typeCoercion.canCoerce() instead of explicit resolution of the operator (metadata.getCoercion()).