[FEAT] Implement wildcard expansion for the current directory

[itislu]

• First merge [FIX] Fix wrong null-expansion after word-splitting and quote combination #283

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Matching filenames

• Neither heredoc content nor heredoc end undergo wildcard expansion.
• * within any quotes should not get expanded and should just match the literal character *.
• If no filenames could be found, or the current directory could not be read from, the string stays unmodified by wildcard expansion.
• Filenames starting with . have to be matched explicitely, like with .*.
• If any character is quoted, the quoted character itself shall be matched.
  This means, even tough filename expansion occurs before quote removal, *"fi"le should not try to match <anything>"fi"le, but <anything>file. (reference)

Order of filenames

The order of the filenames that match exactly immitates bash's sorting order for ASCII characters, following these rules revealed by testing:

1. Numeric characters come before alphabetic characters.
2. Alphabetic characters are compared ignoring case.
3. Lowercase characters come before uppercase characters.
4. If equal alphanumerically, non-alphanumeric characters are given priority.
5. If both are non-alphanumeric, lower ASCII value comes first.

However, bash itself uses a much more complicated system called collation, where each unicode character has specific a place in a list of all characters.
This list can be viewed from this path:

/usr/share/i18n/locales/iso14651_t1_common

For all possible characters from the German keyboard, the order is as follows:

\t\n\v\f\r !"#%&'()*+,-./:;<=>?@[\]^_`{|}~¡§¨©«¬®¯°±´¶·¸»¿×÷ˇˍ˘˙˚˛˝–—‘’‚“”„…′″‹›←↑→↓¤¢$£¥€01¹½¼⅛2²3³⅜45⅝67⅞89aAªäÄæÆbBcCdDđðÐeEfFgGhHħĦiIıjJkKlLłŁmMnNŋŊoOºöÖøØpPqQĸrRsSſßẞtT™ŧŦuUüÜvVwWxXyYzZþÞµΩ

In C there is a function that can handle this collating called strcoll().
For more great information:
https://unix.stackexchange.com/questions/423345/generate-collating-order-of-a-list-of-individual-characters
https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap07.html#tag_07_03_02

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• Known issue: [KNOWN ISSUE] Word splitting and filename expansion should not be performed when assigning values to variables #295

• Resolves [EXPLANATION] Wildcard behavior #107 (many tricky test cases listed in the issue)

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Test cases

export A=$
echo "$A"USER

export A="*"
echo $A""

echo *""file

echo *"f"ile

echo *"*"*

echo *" "*

export B="a  b  c Make"
echo ""$B""*$B*""

echo "*"*""*

echo *"*"*""**

echo "M"*"e"

touch echo file
* 123

[itislu]

@LeaYeh I left the function name as get_next_wildcard() for consistency because we always use get_... for this type of function.
If that's okay, this PR can be merged.