feat(frontend): add stateless two-phase ApproxPercentile

[kwannoel]

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What's changed and what's your intention?

30% the changes in this PR are planner tests + binder tests

This is part of #17531.

We add stateless two-phase simple approx percentile, integrating it with gen_stateless_two_phase_streaming_agg_plan.

StreamLocalApproxPercentile is the local phase for approx_percentile.
StreamGlobalApproxPercentile is the global phase.

We do not implement a core for either of these, since the fields they use are different (global step does not require any parameters, local step requires the parameters). Further, there's also no logical plan node which corresponds to these stream nodes, so there's no need to add a core, it will just be overhead.

We also add KeyedMerge which will combine the results from approx percentile and normal aggs, as well as pair-wise approx percentiles.

• Add stateless two-phase approx percentile.
• Fix the keyed merge schema.
• Handle multiple approx percentiles.
• Fix distribution of global approx percentile.
• Handle DESC approx percentile.
• Planner tests

Subsequent PRs

• Handle vnode based two-phase approx percentile.
• Handle single phase approx percentile (embedded in expr framework).
• Write local approx percentile agg.
• Write global approx percentile agg.

Checklist

• I have written necessary rustdoc comments
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[fuyufjh]

Generally LGTM

[kwannoel]

Any review from @stdrc @st1page ?

[stdrc]

Rest LGTM

[stdrc]

Is it possible to unify ApproxPercentile executor with ApproxCountDistinct to have something like BucketBasedAgg? Just curious, not a suggestion.

[kwannoel]

Hmm I'm not sure about the internals of approx count distinct. Does it involve 2 phase agg?

[stdrc]

No I mean is it possible to abstract a common executor like HashAgg that can do various kinds of aggregation that can fit into the framework. This seems not related to 2-phase agg, cuz HashAgg can be used in either local phase or global phase.