[ES|QL] Improve autocomplete based on context

[dej611]

Describe the feature:

It would be nice to have a better experience with autocomplete, with particular care of context before proposing suggestions to the user.
For instance, here some ideas:

• when the user is typing within a function it would be nice to have suggestions based on the specific function and argument position:

eval then = n + date_trunc( // <= should suggest "1 year" or any other durational unit
eval then = n + date_trunc(1 year, // <= should suggest only fields of type "date" here
eval b = abs( <= should suggest only fields of number type here

• be aware of the "duration" mode in EVAL and provide better suggestions in this context

  • [ES|QL] Add date math syntax and autocomplete support #166058 makes is a bit better for the + and - case, but still need to handle * and /
  • most of the times the fallback suggestion is <fields> while it should be more contextual

  from logstash-* | limit 10 | eval myVar = abs(bytes) * // <= should suggest also functions here
  

• should propose comma options where possible

  • for commands who support it
  • for functions with multiple arguments

...to be updated...

Describe a specific use case for the feature:

[elasticmachine]

Pinging @elastic/kibana-visualizations (Team:Visualizations)

[dej611]

Handled as part of #166242

[dej611]

Closing as solved by #170071