Optional skipping of hidden files/folders in list_files

[yani.iliev]

The function always skips hidden files/folders that begin with a dot (.)
This allows for files like .htaccess and .git to be skipped when listing a folder.
This ticket is about allow to suppress this behavior in the function and return hidden files/folders that begin with a dot (.).
One possible solution is to add a new argument to the function so that the function is defined as such:
function list_files( $folder = '', $levels = 100, $exclusions = array(), $skip_dots = true )

This adds a new optional $include_hidden parameter to allow the inclusion of hidden ("." prefixed) files.

Defaults to false for backward compatibility.

Trac ticket: https://core.trac.wordpress.org/ticket/53659

[costdev]

• ​PR 4223 introduces the $include_hidden parameter to allow the inclusion of hidden ("." prefixed) files.
• The parameter name $include_hidden is used as this is consistent with the parameter name used in the ::dirlist() filesystem abstraction classes, which defaults to true.
• However, this new parameter in list_files() defaults to false for backward compatibility.

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• Hidden file exclusion was introduced in [41806]. See this comment. Setting the Version property to 4.9.
• Milestoning this ticket for 6.3.

[rutviksavsani]

This ticket was discussed in the recent bug scrub.
It seems we need testing instructions/info and testing the PR.