We fallback to legacy WebView in two cases:
* On systems prior to macOS 10.11 (it may be possible to support WKWebView in 10.10, but due to an 10.11+ only API I didn't bother putting in the effort)
* For apps using the downloader XPC service which are most likely sandboxed apps without an outgoing network entitlement. WKWebView doesn't function in that case (FB6993802 - https://github.com/feedback-assistant/reports/issues/1)
Additional notes:
* Added an abstraction for using WebView or WKWebView
* Web view is created and inserted programmatically rather than from the nib which has previously caused issues (and is not allowed for WKWebView prior to 10.12 due to some NSCoding bug).
* We need to rely on WKWebView private API for drawing transparent background (FB7539179 - https://github.com/feedback-assistant/reports/issues/81). Additional notes in the code.
* We always inject a custom stylesheet for dark mode colors and default font family/size (for WKWebView).
* This should also improve the Catalyst support story (#1482)
Pavel MoiseenkoandGitHub
ZorgandKornel