Backport Show non categorized flags with categorized on help

[jetexe]

What type of PR is this?

• bug
• feature

What this PR does / why we need it:

Reverting the removal of visible flags from help if their sibling flags have categories defined.

Example:

App:
    Flags:
        Flag1: // non categorized
        Flag2: Category1
        
Help Before PR:
    Options:
      Category1
        Flag2
        
Help After:
    Options:
        Flag1
      
      Category1
        Flag2

Which issue(s) this PR fixes:

fixes #1672 for version 3

Special notes for your reviewer:

This is a backport (or forwardport in our case) of #1673

Testing

• Unit tests added
• Example application tryed

Release Notes

Reverted removal of non categorized flags alongside categorized flags

[tarampampam]

LGFM