Prevent deleting the nullable type prefix when the "fix imports" is run #7123

[junichi11]

• in PHP "?" being auto removed from typehinting #7123
• Ignore the part of the nullable type prefix
• Add/Fix unit tests

Example

/**
 * @property ?GH7123_01     $test_1
 * @property GH7123_01|null $test_2
 */
class GH7123_01{}

Before:

/**
 * @property GH7123_01     $test_1
 * @property GH7123_01|null $test_2
 */
class GH7123_01{}

After:

/**
 * @property ?GH7123_01     $test_1
 * @property GH7123_01|null $test_2
 */
class GH7123_01{}