PHPLIB-1359 Add tests on Accumulators ($group, $bucket, $bucketAuto, $setWindowFields)

[GromNaN]

Fix PHPLIB-1359

https://www.mongodb.com/docs/manual/reference/operator/aggregation/#accumulators---group---bucket---bucketauto---setwindowfields-

For the operators that have accumulator and expression examples on the same page, I added the examples on both.

• $accumulator already done
• $addToSet already done
• $avg accumulator + expression
• $bottom
• $bottomN
• $count the empty object required modifications in Yaml parsing
• $first already done
• $firstN accumulator + expression
• $last already done
• $lastN
• $max accumulator + expression
• $maxN
• $median accumulator + expression
• $mergeObjects
• $min accumulator + expression
• $percentile accumulator + expression
• $push
• $stdDevPop accumulator + expression
• $stdDevSamp accumulator + expression
• $sum accumulator + expression
• $top
• $topN

[GromNaN]

The option PARSE_OBJECT_FOR_MAP is required to ensure the $count empty object {} from the Yaml is not converted to an empty array. []

[GromNaN]

I think this line of code is "expert" level.

[alcaeus]

Splitting this line across multiple lines may just make it a little less "expert" and help tell the closure apart from the arg:

Suggested change

	$this->tests = array_map(static fn (object $test): TestDefinition => new TestDefinition(...(array) $test), array_values($tests));
	$this->tests = array_map(
	static fn (object $test): TestDefinition => new TestDefinition(...(array) $test),
	array_values($tests),
	);

[GromNaN]

I'm always using the same way to write the pipelines (using object and not array map), so I don't really cover all the feature.

[GromNaN]

This should be an enum.

[alcaeus]

Have one comment for legibility, but LGTM.

As for the topic of enums, I believe there are a couple of other places where we can consider using an enum (e.g. the unbounded and current identifiers for windows). These have the advantage of making possible values easier to discover.

[alcaeus]

Splitting this line across multiple lines may just make it a little less "expert" and help tell the closure apart from the arg:

Suggested change

	$this->tests = array_map(static fn (object $test): TestDefinition => new TestDefinition(...(array) $test), array_values($tests));
	$this->tests = array_map(
	static fn (object $test): TestDefinition => new TestDefinition(...(array) $test),
	array_values($tests),
	);

[GromNaN]

As for the topic of enums, I believe there are a couple of other places where we can consider using an enum (e.g. the unbounded and current identifiers for windows). These have the advantage of making possible values easier to discover.

Since both values are often used together (at least in examples), we may also make an enum that return both.