add option to force v1 postMessage ipc protocol

[thewh1teagle]

It's important to have the ability to control whether to use the old IPC protocol or the newer one. For instance, because the new method uses fetch, we have issues like #8476.

So, I added the ability to force using the v1 postMessage IPC protocol by activating the force-ipc-v1-protocol feature in the Tauri dependency.

I tested it on MacOS / Windows both when activated and not, and it works.
Also it solved for me the CSP issues in windows.

https://discord.com/channels/616186924390023171/1201542436040757248

Update

Looks like it doesn't work on Windows when returning JSON value from rust, checking it. (it works with strings)

Update1

Solved in second commit. need review

[lucasfernog]

I think this should be resolved at runtime instead, so you can have both the v1 and the v2 IPC implementations if you app use both local and remote URLs.

[thewh1teagle]

@lucasfernog

I think it might be much better to handle it at runtime / per webview.
Do you have any ideas for a convenient interface or examples that we could follow?

[lucasfernog]

After investigating this I believe it's easier to handle the CSP issue at the IPC layer instead of letting the user to configure it (with is a lot more complicated). I'll open a PR soon.

Thank you for this PR though, you've done a great job investigating the problem and finding a solution!