feat: implement Set.isSubsetOf() for Node <22, which defaults to builtin implementation whenever possible

[novusnota]

Issue

Closes #1008.

Checklist

• I have updated CHANGELOG.md
• I have run all the tests locally and no test failure was reported
• I have run the linter, formatter and spellchecker
• I did not do unrelated and/or undiscussed refactorings

[verytactical]

Please don't patch any prototypes. Other libraries might expect builtin ES methods to work exactly to the letter of specification, and this implementation doesn't really look like it.

In case something goes wrong, we'll be up to hours of debug, because prototype patching changes behavior of other code remotely and without any trace.

It would be much easier both for implementer and for future users to just define isSubsetOf function, and optionally default it to builtin .isSubsetOf method for increased performance on newer JS engines.

[verytactical]

I should also mention that the concept of "polyfill" relies on the process around it. Polyfills are supplied by well-tested libraries, their authors are well-versed in spec legalese, and, most importantly, polyfills are applied by build infrastructure (for example, babel). Due to wider adoption of those polyfills, we reduce detection time for inevitable bugs in their implementations, and get centralized updates and security audits.

In this context neither the word "polyfill" nor its implementation appears as something end user might encounter in production codebase. At least not under regular circumstances.

[novusnota]

@verytactical I generally agree against prototype patching, but thought this particular case might be fine. Plus, I simply took the working polyfill from Web IDE repo. Which, I suppose, was in turn taken from core-js. Or not :)

Anyways, I can re-write one or another implementation as a global function with optional fallback to the builtin method if/when it's present

[verytactical]

Please, define it as a function.

In case of WebIDE it's apparently either used in one of the libraries, or not used at all. Probably it's there, because it compiles code with tact, and with this PR it won't be needed anymore. Unfortunately I don't know circumstances of when it was added.

cc @rahulyadav-57

[novusnota]

@verytactical all good now — the function is global, but your introduction of fs.glob in scripts/copy-files.ts has tied us to Node.js 22 :)

UPD: Turns out we do have the glob package used elsewhere, so I just replaced fs.glob() with glob.sync()

[verytactical]

I think I should stop bikeshedding this :)

[verytactical]

.