fix(ios): fix URL resolution when external frameworks are loaded

[daniellacosse]

I'm not 100% sure if this fixes the issue I was encountering in all cases but here's the lowdown:

I'm loading an xcframework compiled by gomobile into the xcode project that Capacitor creates. There was this mysterious behavior where as soon as I called any function exposed by that library, my app wouldn't load and I'd get the following error:

[pageProxyID=16, webPageID=17, PID=50534] WebPageProxy::didFailProvisionalLoadForFrame: 
frameID=1, isMainFrame=1, domain=NSCocoaErrorDomain, code=256, isMainFrame=1, 
willInternallyHandleFailure=0

I traced the source of the error to this Router.swift file and discovered that when I didn't call any gomobile-compiled function, the result of pathUrl was different. According to the Swift Foundation source, URL(fileURLWithPath:)

    /// Initializes a newly created URL using the contents of the given data, 
relative to a base URL.

So it seems that somehow (I don't fully understand it), accessing the .xcframework in the running code changes the base URL that URL(fileURLWithPath:) starts from. By adding the basePath in here, I think we're now enforcing a consistent URL base, and my app appears to work now whether I call a method from my library or not.

Here is a photo of it working with the fix: