feat(Spanner): Support FGAC

[ajupazhamayil]

This PR add the FGAC support for PHP Spanner library.

The FGAC integration tests are skipped in the emulator since it has not yet implemented the FGAC support.

Other languages also skips the same. Ref: https://github.com/googleapis/google-cloud-ruby/pull/19067/files#diff-3bf69404604fe1c87333533412f6e24d5867aab51a726e98843ebd63cd39b3a5R28

[vishwarajanand]

Pls fix the formatting, docblocks and test changes requested.

[vishwarajanand]

In my local env, php8.1, for pre-existing tests parsing V1/Session object fails at

google-cloud-php/Spanner/src/Connection/Grpc.php

Line 781 in 7e1b3d4

$args['session'] = $this->serializer->decodeMessage(new Session, $session);

when creator_role is null. Do you think we should add array_filter over here:

google-cloud-php/Spanner/src/Operation.php

Lines 564 to 567 in 50f0759

	'session' => [
	'labels' => $this->pluck('labels', $options, false) ?: [],
	'creator_role' => $this->pluck('creator_role', $options, false) ?: null
	]

[vishwarajanand]

Changes looks good to me now, thanks for diligently resolve all comments.
Only 2 changes pending: array_filter styling and rebase with main.

[vishwarajanand]

LGTM