feat: Create anchor target type plugin for xhtml

[jtoloui-ibm]

Add support for target type in anchor tag xhtml

To support target type in xhtml links

• Included select option: _blank, _self, _top, _parent
• When enabled it will replace the link toolbar action and use the recreated version with target type support
• Enabled attaching of Target value in xhtml.js

[jtoloui-ibm]

I was struggling to assign an icon to replace the link would you be able to suggest the best way to fix this? For the moment i've just used the format one

[jtoloui-ibm]

Hey @samclarke, please let me know if this format is okay as a plugin

[jtoloui-ibm]

Hey @samclarke, hope you're doing well. Was just wondering if this PR is okay for the next minor version for a plugin.

[samclarke]

Thanks for the PR. It looks good! Sorry for the delay in reviewing it.

Could you revert the package-lock.json file to the master branch version? The default behaviour of npm install annoyingly rewrites (have to use npm ci to avoid that).

[samclarke]

It might be worth adding a check to see if this plugin is loaded as we probably don't want to allow other targets if it isn't.

There isn't a way to check from here as the converters don't have access to have but could check for if this plugin exists:

if (sceditor.plugins.anchortarget ...