bsdinstall docsinstall: Replace dialog(1) with bsddialog(1)

[asiciliano]

Summary

Replace dialog(1) with bsddialog(1). Delete f_dialog_checklist_size() because it is not suitable for bsddialog, instead use bsddialog(3) autosize. The checklist could overlay the backtitle "FreeBSD Installer" with little screen, the problem is fixed in upstream {*}, it will be availble in the next import or now if somebody will require this feature.

{*}
lib : add conf.auto_topmargin and conf.auto_downmargin
utility: fix: overlay backtitle and overlay shadow below

Test Plan

Checklist is tested already.

┌───────┤FreeBSD Documentation Installation├───────┐
│ This menu allows you to install the whole        │  
│ documentation set from the FreeBSD Documentation │  
│ Project: Handbook, FAQ, and articles.            │  
│                                                  │  
│ Please select the language versions you wish to  │  
│ install. At minimum, you should install the      │  
│ English version, the original version of the     │  
│ documentation.                                   │  
│ ┌──────────────────────────────────────────────┐ │  
│ │ [ ] bn    Bengali Documentation              │ │  
│ │ [ ] da    Danish Documentation               │ │  
│ │ [ ] de    German Documentation               │ │  
│ │ [ ] el    Greek Documentation                │ │  
│ │ [X] en    English Documentation (recommended)│ │  
│ │ [ ] es    Spanish Documentation              │ │  
│ │ [ ] fr    French Documentation               │ │  
│ │ [ ] hu    Hungarian Documentation            │ │  
│ │ [ ] it    Italian Documentation              │ │  
│ │ [ ] ja    Japanese Documentation             │ │  
│ │ [ ] ko    Korean Documentation               │ │  
│ │ [ ] mn    Mongolian Documentation            │ │  
│ │ [ ] nl    Dutch Documentation                │ │  
│ │ [ ] pl    Polish Documentation               │ │  
│ │ [ ] pt    Portuguese Documentation           │ │  
│ │ [ ] ru    Russian Documentation              │ │  
│ │ [ ] tr    Turkish Documentation              │ │  
│ │ [ ] zh_cn Simplified Chinese Documentation   │ │  
│ │ [ ] zh_tw Traditional Chinese Documentation  │ │  
│ └──────────────────────────────────────────────┘ │  
├──────────────────────────────────────────────────┤  
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[blackend]

Thanks.

[asiciliano]

Abandon: this replacement can be implied just by changing the $DIALOG variable in bsdconfig.