[FEAT] Input for custom set of special characters

There isn't a universal consensus on what constitutes the set of ”special characters” that can be used in a password. Various password-protected sites (banks, etc) have different sets of special characters that are permitted in passwords for their site. Oftentimes they will exactly specify which special characters they allow. Some sites might allow all of these
!"#$%&'()*+,-./:;<=>?@[]^_`{|}~
... while other sites might only allow a dozen or so. The set varies from site to site.

I'd love to see a text box within the Generate Password section that would allow users to paste a set of special characters that has been copied directly from the site for which a password is being created. These would then be randomly mixed with other permitted characters, probably alphanumeric, to create a valid password. (It would be a good idea to automatically remove spaces from the set of special characters after it has been pasted in.)

Using the current system, passwords often need to be carefully manually edited to remove a few offending special characters. Copying and pasting the set of special characters that is specifically needed would allow users to create passwords more easily and quickly.

Start by locating the Generate Password section and the existing password character-generation entry point. Trace how special characters are currently selected, then verify that a pasted custom set can be accepted, spaces are removed, and generated passwords use the permitted characters.