Replace the ES5-era claims in the README

[lahma]

The README still says Jint "is fully ECMAScript 5 compatible" and lists "Support of ES5 through Jint" as the headline feature. Jint has implemented ES2015 through ES2025 for several releases (we are on 4.15.3), so the README understates what scripts this binding can actually run — a reader evaluating AngleSharp.Js for a page built with classes, modules or async/await would conclude it cannot handle them.

What changed

• Vision and Status now states the ES2015–ES2025 range with a handful of concrete features, and links to Jint's own feature matrix rather than restating a version number here that will go stale again.
• The same paragraph mentions that type="module" and type="importmap" scripts are evaluated, which JsScriptingService.SupportsType has accepted for a while but the README never said.
• Features replaces the ES5 bullet, adds ES modules / import maps and Web Workers (both shipping in 1.0.0 per the changelog), and replaces "Evaluation of simple scripts (incl. jQuery)" with the libraries the suite actually runs.

Verification

I did not want to copy Jint's feature list on faith, so I ran the claims through this binding layer as script — private class fields, async/await, generators, optional chaining with ??, spread of a Set, template literals, Proxy/Reflect/BigInt/Symbol, Object.groupBy (ES2024) and Set.prototype.union (ES2025) all evaluate correctly through EvalScriptAsync, as does destructuring a spread querySelectorAll result. Those probes were scratch tests and are not part of the diff.

Documentation only — no CHANGELOG.md entry, since nothing in the package changed. docs/ carries no comparable stale claim; the only ES5 references in the repository were the two in the README.

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