feat: modify rules on the fly

[hirasso]

Description

On large websites or in complex cases it could come in handy to be able to modify fragment rules on the fly. This PR is adding a few new API functions:

/** Keep a reference to fragment plugin during instanciation */
const fragmentPlugin = new SwupFragmentPlugin({ rules });
new Swup({ plugins: [fragmentPlugin] });

/** Higher-Level methods: */

/** Prepend a fragment rule */
fragmentPlugin.prependRule(rule);

/** Append a fragment rule */
fragmentPlugin.appendRule(rule);

/** Lower-Level methods: */

/** Get a structured clone of the current rules */
fragmentPlugin.getRules();

/** Update the fragment rules */
fragmentPlugin.setRules(rules: Rule[]);

Questions

Is structuredClone ready to be used?

Checks

• [x] The PR is submitted to the master branch
• [x] The code was linted before pushing (npm run lint)
• [x] All tests are passing (npm run test)
• [x] New or updated tests are included
• [ ] The documentation was updated as required in #59

[hirasso]

@daun ready for review :)

[daun]

API looks great! Is there an alternative for structuredClone that has been supported for a little longer? When creating sites with a two-year browser support window, it will require a polyfill that adds a few kilobytes. Or maybe the plugin could check if structuredClone is supported and only use it if found, otherwise do a shallow copy?

[hirasso]

Hmm, right... I think I'll go with a detection for structuredClone and otherwise return a shallow copy, combined with a warning if options.debug is true

[hirasso]

...turns out cloning the rules by myself wasn't so hard, as it's structure is well known. structuredClone dependency is gone!