Ticket #3160: Use new colors for listbox's selected entry

[egmontkob]

Proposed changes

Introduce new colors dselnormal and dselfocus for unfocused and focused
listbox's selected entry, forked off from the here misused dfocus and
dhotfocus, respectively.

Adjust skins not the underline listbox's selected entry.

• Resolves: Dialog hotfocus color misused in listbox #3160

Checklist

👉 Our coding style can be found here: https://midnight-commander.org/coding-style/ 👈

• I have referenced the issue(s) resolved by this PR (if any)
• I have signed-off my contribution with git commit --amend -s
• Lint and unit tests pass locally with my changes (make indent && make check)
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation (if appropriate)

[egmontkob]

This change, if accepted, will slightly break the look of 3rd party skins, they'll need to be adjusted to introduce these two new colors. This won't be the first, nor the last such occasion, since we don't have proper fallback / compatibility mechanism in place.

I updated the skins using this quick-n-dirty one-off script:

#!/bin/bash

while IFS='' read line; do
  echo "$line"

  if [[ $line =~ " dfocus" ]]; then
    dfocline="$line"
  elif [[ $line =~ " dhotfocus" ]]; then
    dhotfocline="$line"
  fi

  if [[ $line =~ " dhotfocus" ]]; then
    echo "${dfocline/dfocus/dselnormal}"
    echo "${dhotfocline/dhotfocus/dselfocus}"
  fi
done <$1 >$1.tmp

mv "$1.tmp" "$1"

[egmontkob]

I did not touch the documentation, nor the supported keywords for the --colors cmdline option. See #4908.