Provide a drush command upgrade path for 3x to 4x to convert from [fn] and <fn> to the new modal window

Works for simple use cases, thanks.

Problems:
1. Where content creators have added space at start and end of footnote text, inside tags, this space needs to be removed. Footnotes 4.x converts that space to

tags, and 3.x does, so our content creatores often wrap text in line breaks for clearer layout of HTML layout. Content creators do not want the upgraded footnotes to add a paragraphs at start and end of footnotes, where 3.x had none.

2. The drush command converts ' fake apostrophes to HTML entity references but does not covert real apostrophes ’ (which some fonts print as forward sloping ticks). Our content creators prefer real apostrophes even though standard English keyboards do not have a key for them. So long as normal punctuation breaks Footnotes 4.x, and #3414604: Support adding the text content within the <footnotes> element remains unfixed, all punctuation which breaks footnotes would need to be converted by an upgade command.

Here is a piece of HTML outputted by the drush command.

<footnotes data-value="" data-text="@Malaria Consortium’s seasonal malaria chemoprevention program: Philanthropy report 2020@, Pg. 5."></footnotes>

I don't what the expected output is. I do know that the inclusion of a real apostrophe in Consortium’s as distinct from a fake / keyboard apostrophe, is enough to break footnotes when using 4.x but not when using 3.x.

You can see an example of the extra space at start and end of the footnote text at https://www.drupal.org/project/footnotes/issues/3414604#comment-15397449. If 4.x. is going to turn this extra space into <p> tags, in a way that 3.x. did not, that space should be removed, and documetation should warn content creators to stop adding such space for clearer layout in their HTML source editing window.

Many thanks. I finally got round to testing. Sorry about the delay.

This does not work where there is a line break before the start of the footnote text.
For example, this works:
Here is some body text.<footnotes data-value="">Here is some footnote text.</footnotes>

When editors are working without WYSYWIG, they will add line breaks for better layout.

Here is some body text.<footnotes data-value="">
Here is some footnote text.
</footnotes>

Editors may also add line breaks within footnote text. For example:

Here is some body text.<footnotes data-value="">Here is some footnote text.
Here is some more footnote text, which should appear after a line break.

Here is a second paragraph of footnote text.</footnotes>

When using the above, including one or more line breaks before, after, or within the footnote text, the footnotes are empty. DBlog says Warning: DOMDocumentFragment::appendXML(): ^ in Drupal\footnotes\Plugin\Filter\FootnotesFilter->process() (line 161 of /home/website/dev_html/web/modules/contrib/footnotes/src/Plugin/Filter/FootnotesFilter.php)

Enabling / disabling the 'convert line breaks to p tags' filter makes no difference.

Separate issue, but I am also concerned if we upgrade footnotes using this drush command, and a year later the content creators decide they want to start using CDEditor.