Enhancement: Checking that text in SVG is searchable

[ajeanmahoney]

It would be nice if svgcheck warned about strings that are not searchable. For example, said something like "Warning: SVG appears to contain a text string that has been separated into letters. Ability to select text or search for text within the image may be affected." These usability issues can then be addressed by authors and editors (SVG updated or alt text provided, etc.).

Some background

Some examples:

• https://www.rfc-editor.org/rfc/rfc8899.html (text is selectable-ish but gets scrambled when copy and pasted; is not searchable)
• https://www.rfc-editor.org/rfc/rfc8989.html (text is selectable and searchable)
• https://www.rfc-editor.org/rfc/rfc9043.html (text is neither)
• https://www.rfc-editor.org/rfc/rfc9100.html (text is neither)
• https://www.rfc-editor.org/rfc/rfc9115.html (text is selectable but gets scrambled when copy and pasted; is not searchable)
• https://www.rfc-editor.org/rfc/rfc9216.html (text is selectable and searchable)

The workaround is to manually search for strings that are used in the SVG diagram and to use a mouse cursor to see if text in an SVG diagram can be selected.