Add webviews as separate browsers

Relevant links:

• webview community group: https://github.com/WebView-CG
• mdn adding data for webview_ios : https://github.com/mdn/browser-compat-data/pull/23747
• list of browsers showing webview_ios and webview_android : https://github.com/mdn/browser-compat-data/tree/main/browsers

The core idea seems to be that webviews often have the same underlying engine as the core browser of each respective platform but doesn't have feature parity.

The difference in supported features is now being tracked by MDN browser compat data.

Ideally it would be possible to craft browserslist queries for these as well.

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I now mostly use mdn data for both cssdb (postcss-preset-env) and polyfill-library. But autoprefixer uses caniuselite, right?

Is adding support for webview_ios and webview_android in browserslist dependent on it also being upstreamed in caniuse?