Create check to verify that @see internal function reference is valid

Problem/Motivation

There are @see references in Drupal core to something that no longer exists in core.

An @see reference that does not exit.
\Drupal\Core\TypedData\ListInterface has this line and that class does not exist.
* @see \Drupal\Core\TypedData\ListDefinitionInterface

An @see reference that does exit.
\Drupal\Tests\Core\Database\Stub\StubPDO has this line which does exist.

@see Drupal\Core\Database\Connection

Steps to reproduce

Proposed resolution

Create a code check or sniff to verify that within a @see reference that an internal reference to a function or class method actually exists. Because the code will need to perform the equivalent of calls to function_exists() or method_exists(), this may require an addition to the Coder Review rather than a code sniff.

Tests:

• Symbol (e.g., function, method) exists.
• Symbol does not @see itself. (Example: #2621516: hook_page_attachments_alter() @see's itself instead of hook_page_attachments())

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet