Add enum support in ArrayHelper::toArray()

[WarLikeLaux]

Q	A
Is bugfix?	✔️
New feature?	❌
Breaks BC?	❌
Fixed issues	#20065

What does this PR do?

Fixes enum handling in ArrayHelper::toArray(). BackedEnum resolves to ->value, UnitEnum resolves to ->name.

Before:

ArrayHelper::toArray([Status::Active, Status::Inactive]);
// [['name' => 'Active', 'value' => 1], ['name' => 'Inactive', 'value' => 0]]

ArrayHelper::toArray(Status::Active);
// ['name' => 'Active', 'value' => 1]

After:

ArrayHelper::toArray([Status::Active, Status::Inactive]);
// [1, 0]

ArrayHelper::toArray(Status::Active);
// [1]

Enums inside arrays resolve to scalar values directly. Single enum is wrapped in array to preserve the @return array contract - same as toArray('foo') returns ['foo'].

How other frameworks handle this

• Symfony - BackedEnumNormalizer returns ->value (scalar). Source
• Laravel - Eloquent casts enum attributes to ->value on toArray(). Source
• Yii2 (current) - iterates enum as generic object, leaks internal structure: ['name' => 'Active', 'value' => 1]
• PHP json_encode - BackedEnum serializes to its scalar value natively

All major frameworks resolve enums to scalar values. The current Yii2 behavior is a side effect of generic object iteration - enums were not handled explicitly, so toArray() leaked their internal structure (name/value properties) instead of extracting the meaningful value.

Alternative to #20065, which only handled UnitEnum and had no tests. This PR also handles BackedEnum separately, is compatible with PHP 7.4/8.0 (tests skipped, phpstan clean on both configs), and includes 6 unit tests.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.57%. Comparing base (379b296) to head (743afc5).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff            @@
##             master   #20781   +/-   ##
=========================================
  Coverage     78.56%   78.57%           
- Complexity    11568    11576    +8     
=========================================
  Files           376      376           
  Lines         30750    30758    +8     
=========================================
+ Hits          24160    24168    +8     
  Misses         6590     6590           

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