[canvas] remove filters function

[ppisljar]

Canvas implements filtering a bit different than the rest of kibana:

• panels (renderers) can be added to canvas, which can create filters and add them to canvas store
• filters expression function reads from canvas store to get the stored filters which are in form of expressions
• those expressions are executed to get a canvas Filter structure which is a linked list of canvas filters
• canvas data fetching functions can convert that filter structure to DSL

On the other hand this is how it works in the rest of kibana:

• panels (renderers) or other components and emit an UI action with kibana Filter[] structure
• those kibana Filters will be added to the filtermanager (store)
• filters from filter manager are passed to expression executor as part of a SearchContext
• kibana_context reads from SearchContext and can also add custom filters to it
• remove_filter and select_filter functions allow further subselection of filters by group or owner
• data fetching functions can use that kibana Filter[] structure to generate queries

even if the second sounds a bit more complicated it brings us several benefits:

• not linked to a single consumer, can work across different applications
• works on the server
• better flexibility

This are the steps canvas would need to take to adopt the same filtering approach other apps are using:

• update canvas store to hold kibana Filter[] structure instead of array of filter expressions
• update renderers that update the store to write out correct structure
  (the code for all this is already there as you already convert your filters to kibana filters for the sake of embeddables)
• (optional) update renderers to not write to store directly but rather emit applyFilterAction and either use default action and read filters from filterManager or (less preferred) write custom action that updates your store
• update your calls to executor to pass in SearchContext with filters array
• update your logic generating expressions so that instead of filters you output kibana_context | select_filter
• add migration for filters function which should rewrite filters .... to kibana_context | select_filter ...
• add migration for your store, which will parse filter expressions and convert them to kibana Filter structures
• remove timeFilter and exactly functions (or rewrite them to output kibana Filter structure)
• update your data fetching functions to work with KibanaContext input type [Canvas] Adding support of kibana_context to datasource expressions. #121859

possibly you would want to take some shortcuts and avoid some migrations (less preferred)

• don't update your store, dont update your rederers, don't update your expression functions
• update your calls to executor so that you first run your filter expressions to get your filter structures then convert those to kibana filters using build_embeddable_filters and pass this in as SearchContext.filters
• update your expression generating logic (and add migration) to convert filters to kibana_context | select_filter

[dokmic]

As discussed in #141526 and #121859, the filters function can be safely removed when those items are completed. Since the function is in the canvas plugin now, I think it makes sense for @elastic/kibana-presentation to take care of the whole migration/deprecation process.

[ThomThomson]

Closing this as we are currently not able to prioritize high-effort work that aligns Canvas with the rest of Kibana.