feat(sql): add auxiliary meta functions to support integration with third party library superset

[marregui]

Two new functions keywords and functions to support statements such as:

SELECT name, count(name) as overrides, type FROM functions() GROUP BY name, type ORDER BY name;
SELECT * FROM keywords();

Function keywords()

Returns a list of all keywords supported by QuestDB:

keyword
======
add
all
alter
and
as
asc
asof
...

Function functions()

Returns a table with headers:

• name: name of the function
• signature: signature of the function, there will be one per function override
• signature_translated: as above but human readable. It takes the signature as described by each implementation and translates the individual characters into human readable strings with prefix const if the parameter must be a constant expression.
• runtime_constant: whether it has been declared as a runtime constant.
• type: one of
  • PREDICATE: a boolean function as defined by FunctionFactory.
  • CURSOR: a cursor function.
  • GROUP_BY: a group by function.
  • WINDOW: a window function.
  • STANDARD: whenever it is non of the above

Example rows:

| name   | signature   | signature_translated                             | type             |
| length  | length(U)   | length(var binary)                                  | STANDARD |
...
| rnd_int | rnd_int()    | rnd_int()                                                 | STANDARD |
| rnd_int | rnd_int(iii) | rnd_int(const int, const int, const int) | STANDARD |
...

Implementation notes

I moved the construction of the FunctionFactoryCache into the CairoEngine, and simplified some signatures.

[marregui]

@bziobrowski thank you for the review :) nice spot the use of a sink ;) (I suppose I did no recall that!! dirty garbage!, too long in Python hahaha)

[ideoma]

[PR Coverage check]

😍 pass : 201 / 220 (91.36%)

file detail

	path	covered line	new line	coverage
🔵	io/questdb/griffin/engine/functions/catalogue/KeywordsFunctionFactory.java	29	35	82.86%
🔵	io/questdb/griffin/SqlCompiler.java	8	9	88.89%
🔵	io/questdb/griffin/engine/functions/catalogue/FunctionListFunctionFactory.java	108	118	91.53%
🔵	io/questdb/griffin/FunctionFactoryDescriptor.java	47	49	95.92%
🔵	io/questdb/griffin/FunctionFactoryCache.java	4	4	100.00%
🔵	io/questdb/cairo/CairoEngine.java	3	3	100.00%
🔵	io/questdb/ServerMain.java	2	2	100.00%

[bziobrowski]

Looks good !