feat: Add a way to launch WebViews as incognito WebView::as_incognito, closes #908

[Hyphrio]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

Checklist

• This PR will resolve Launch Webviews as incognito #908
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary
• It can be built on all targets and pass CI/CD.

Other information

This adds an option for WebViewBuilder to allow launching a WebView on incognito mode, to allow for things that would need epheremal instances, such as webview sign-ins.

[Hyphrio]

Currently I only implemented this on Windows and WebKitGTK, I don't have a Mac or an iPhone so I can't do WKWebView that would be guaranteed to work and my computer is too slow to implement Android.

[Hyphrio]

Android would be unsupported as incognito mode would have to be called on the destructors and the non-destructor API is depreciated.

Only thing now is I hope MacOS functionality could be verified as working as I can't test it.

[wusyong]

@Hyphrio It's okay to leave Android unsupported. Thank you for the work! I'll test them all once I get back.

Btw I can't figure out how your example works. Can you elaborate?

[Hyphrio]

Uh the example is unfortunately still broken (on Windows) because of read-only access on the HTML file, I'll probably just spin up a temp HTTP server to work around that but that example just sets a cookie then when you close the window and reopen it it should attempt to load that cookie, but since it's incognito it will appear as nothing

EDIT: Example works on Linux Nevermind it doesn't

[Hyphrio]

WebKitGTK impl is currently broken so I converted this back to draft

[Hyphrio]

Hopefully Linux is fixed now (is_ephemeral was read-only, had to modify both WebContext and WebContextImpl to add a new function named new_ephemeral)

[pewsheen]

Hello @Hyphrio, I can help test if the Mac fix works.

So I just ran the incognito example, the solution with data store configuration works pretty well, but a few things need fixing.

The data store can be retrieved directly from the WKWebsiteDataStore class:

let data_store: id = msg_send![class!(WKWebsiteDataStore), defaultDataStore];
let data_store: id = msg_send![class!(WKWebsiteDataStore), nonPersistentDataStore];

And the data store can be set to WKWebViewConfiguration by calling setWebsiteDataStore from the configuration instance:

let () = msg_send![config, setWebsiteDataStore: data_store];

[Hyphrio]

Alright @pewsheen thank you for the insight about WKWebView!

[wusyong]

I want to make a note on Linux side. So the cookie is persist if we specify a web context even with incognito is enabled.
So I think it will have to skip creating webcontext if we want to use incognito mode.

I'll test macOS and windows later.

Edit: Windows seems great. So it's only macOS left.

[wusyong]

I'm happy with how this turns out. Thank you @Hyphrio!