Add option to omit empty arrays from Arr::dot()

[johnstormentswe]

Adds an optional $preserveEmptyArrays parameter (default true) to Arr::dot() that, when set to false, omits keys whose values are empty arrays from the flattened output.

Default behavior is unchanged — existing callers continue to receive empty arrays preserved as [].

Closes #57305

Example

$data = ['foo' => 'bar', 'tags' => [], 'user' => ['name' => 'Taylor', 'roles' => []]];

Arr::dot($data);
// ['foo' => 'bar', 'tags' => [], 'user.name' => 'Taylor', 'user.roles' => []]

Arr::dot($data, '', INF, false);
// ['foo' => 'bar', 'user.name' => 'Taylor']

This makes the result directly usable with array_diff() and other functions that don't handle nested arrays.

Test plan

1. Added testDotOmittingEmptyArrays covering top-level, nested, and depth-limited cases
2. Existing testDot / testDotWithDepth still pass (82 assertions, 495 total)
3. vendor/bin/pint clean

[taylorotwell]

Thanks for your pull request to Laravel!

Unfortunately, I'm going to delay merging this code for now. To preserve our ability to adequately maintain the framework, we need to be very careful regarding the amount of code we include.

If applicable, please consider releasing your code as a package so that the community can still take advantage of your contributions!