Select plugin no longer allows relative apiUrl values

[delfuego]

Summary

When using the select plugin, relative apiUrl values throw an error

Steps to Reproduce

1. Create a select element with a relative apiUrl (e.g., /private/api/something).
2. Initialize the select element.

When you do this, the initialization now throws an error on the first attempt to load data from the API:

TypeError: Failed to construct 'URL': Invalid URL

Demo Link

https://preline.co/plugins/advanced-select.html#js-data-options

Expected Behavior

I would expect that relative URLs should work.

Actual Behavior

It looks like the issue is that v3.1.0 of the plugin used the apiUrl as-is:

preline/src/plugins/select/index.ts

Line 1158 in 069c821

let url = this.apiUrl;

Beginning in v3.2.0 (and in all versions after), the plugin now creates a new URL object from the apiUrl value, which fails because the URL constructor does not accept relative URL paths:

preline/src/plugins/select/core.ts

Line 1613 in 1cd9636

const url = new URL(this.apiUrl);

Given that this is running in the browser context, this could almost certainly be resolved by first using URL.parse to test whether the apiUrl value is parseable as-is, and if not, then trying to construct it with the current page's base URL:

let url;
if (URL.parse(this.apiUrl)) {
   url = new URL(this.apiUrl);
} else {
   url = new URL(this.apiUrl, window.location.origin);
}

Screenshots

No response

[delfuego]

Note that my submitted PR has a slightly different solution than my suggestion above; URL.parse() isn't available in a lot of middle-aged browsers, so my PR avoids using it and keeps using new URL() so that there's no change in browser compatibility.