Deprecate custom schema options

[morozov]

Custom schema options effectively duplicate the functionality of platform options:

dbal/src/Schema/Column.php

Lines 432 to 447 in 541e9dd

	public function toArray()
	{
	return array_merge([
	'name' => $this->_name,
	'type' => $this->_type,
	'default' => $this->_default,
	'notnull' => $this->_notnull,
	'length' => $this->_length,
	'precision' => $this->_precision,
	'scale' => $this->_scale,
	'fixed' => $this->_fixed,
	'unsigned' => $this->_unsigned,
	'autoincrement' => $this->_autoincrement,
	'columnDefinition' => $this->_columnDefinition,
	'comment' => $this->_comment,
	], $this->_platformOptions, $this->_customSchemaOptions);

I didn't even know they exist until they were used in an issue reproducer (#5338 (comment)).

As of #4746, platform options are used for schema comparison:

dbal/src/Platforms/MySQL/Comparator.php

Line 56 in 1809a91

$options = $column->getPlatformOptions();

But custom schema options aren't, so those who use them to define the schema will likely experience issues with schema comparison.

[greg0ire]

Suggested change

	The following `Column` class properties and methods been deprecated:
	The following `Column` class properties and methods have been deprecated: