ESQL: Add pre and post filter for grouping operator

[costin]

Description

Grouping (STATS) command can be quite expensive, whether for processing data coming in (creating groups) or out (number of buckets), etc...
This problem can be alleviated by allowing pre and post filters, both for individual aggs and grouping keys on the grouping command to drop the data as soon being read or is being produced.
Example of pre-filter (see #110821):

FROM index | STATS a_avg = AVG(a) WHERE a > 10, avg = AVG(a)  BY g

Example of post-filter:

FROM index | STATS c = count(*) by g | WHERE c > 10

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)

[nik9000]

From a compute engine standpoint it feels like we could do:

-void addRawInput(Page page);
+void addRawInput(Page page, BooleanVector);

That should be easy to make the code generation stuff build. That's be super easy to specialize into constantAll, constantNone, and variable. We can make those BooleanVectors out of the expression trees easy enough.

[costin]

Since the bool is used only for filtering, there's no need for MV or null handling - how about using a simple bitset instead ?

[nik9000]

For pre-filtering:

• ESQL: Method to convert BooleanBlock to a "mask" #112253
• ESQL: Add way for Block to keepMask #112160
• Compute engine work to apply mask to grouping aggs ESQL: Compute support for filtering grouping aggs #112476
• Compute engine work to apply mask to non-grouping aggs ESQL: Compute support for filtering ungrouped aggs #112717
• Tests for all aggs when filtered
  • ESQL: Fix filtering all elements in aggs #113804
  • Tests for each agg when filtering some rows. ESQL: Test partially filtered aggs #114510
• Plug filtering into language ESQL: Introduce per agg filter #113735
• Plug warnings from filters into warnings infrastructure and test