Refactored VMenu::ShowMenu and its vicinity.

[MKadaner]

Summary

Refactoring in preparation for #711.

References

• Added AlignAnnotations to VMemu. #711

Checklist

• I have followed the contributing guidelines.
• I have discussed this with project maintainers:
  
  If not checked, I accept that this work might be rejected in favor of a different great big ineffable plan.
  

Details

Sorry, it is large, but I believe overall the code is cleaner and easier to understand.

CodeFactor is complaining, and probably rightfully so. On the positive side, one issue is fixed.

[alabuzhev]

It looks way too complex for a thorough review :)
I trust you spent quite some time debugging it and know what you're doing, so the comments will likely be only about technical details & style.

[MKadaner]

[T]he comments will likely be only about technical details & style.

I addressed all comments so far. Could you please check them and resolve whatever looks good?

I trust you spent quite some time debugging it and know what you're doing...

Well, yes, but... Thorough testing is difficult and time consuming.

@rohitab, if by any chance you can spend some time testing this change, I would hugely appreciate it. The change affects all kinds of vertical lists: menus, histories, Find All, comboboxes... The bugs are expected with vertical layout (irregular movement of selection or items, unexpected empty lines, etc.) and with drawing list borders.

I will of course test more during the long weekend. Just now, I noticed one glitch. Find File -> Code Page Combobox may appear something like this (note the mangled left border; if there is no scrollbar, the right border should look similar):

Using code page:    
Automatic detection 
┌───────────────────
├  1201 │ UTF-16 (Bi
├───────┼───────────
├  37   │ IBM EBCDIC
├  500  │ IBM EBCDIC
├  708  │ Arabic - A
├  720  │ Arabic - T
├  737  │ OEM - Gree
│  775  │ OEM - Balt
└───────────────────

I guess I know how to fix this one (even two ways). Will do during the weekend as well.

[MKadaner]

Fixed everything, including the bug with vertical borders.

Not squashing yet to make verification of the comments easier. Also, I want to test a bit more.

Please let me know if everything is OK.

[alabuzhev]

The change looks good, although I haven't tested it.

Thorough testing is difficult and time consuming.

Indeed. We're not in a hurry, so if you'd like to have another look or play more with it, please take your time, we can get back to it next year :)

[MKadaner]

Thank you for the approval. I have been playing with it today for an hour or so and could not find any new issues. Let's call it a day.

I rebased and squashed. Please merge.

[alabuzhev]

Ok. Thank you.

[sonarcloud]

Quality Gate passed

The SonarCloud Quality Gate passed, but some issues were introduced.

14 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[rohitab]

@MKadaner sorry I wasn't able to respond sooner. I am going to upgrade to this version and will let you know if I come across any issues.

[MKadaner]

@rohitab, no problem at all. Your feedback is welcome at any time. When you upgrade, please pick the latest version. I pushed one more refactoring in the same area, drawing of the vertical lists to be more specific. The behavior should not be affected.