Invalid @see links to other structural element generated

[Stefanius67]

Invalid @see links to other structure elements are generated if the structure element is not found in the current documentation for several reasons:

• the link refers to any source that is not included in the project
• a simple spelling mistake or 'letter spreader'
• The target is hidden by the --visibility parameter

Expected behavior

• Do not generate an invalid link (in this case it may be useful to only output the name of the target element.)
• Generate an entry in the error list (if possible including the information if the link is valid but is hidden by the visibility)

Actual behavior

• an invalid link is generated
• no information in the error list

Steps to reproduce the problem

• Insert any @see Tag with invalid method
• Insert @see to an protected element and set --visibility=public

Your environment

• Version used: 2e1ed05
• Install method: PHAR from gitHub
• PHP version: 7.4
• Operating system and version: Ubuntu 20.04