Add WebView versions for api.XRSessionMode.immersive-ar

[queengooborg]

This PR adds real values for WebView Android for the immersive-ar member of the XRSessionMode API, based upon manual testing.

Test Code Used: Copied data from Chrome Android

[foolip]

If https://developer.mozilla.org/en-US/docs/Web/API/Navigator/xr is right XR isn't supported on WebView. Can you check which is right?

[queengooborg]

XR is not supported on WebView, yes, however this is an interface that slipped through the cracks and is still exposed (even if in error), so I'm going off of that. There's a few of these interfaces that are a part of a larger feature set that is mostly disabled, but then there's ones like this that weren't added to not-webview-exposed.txt.

[foolip]

XRSessionMode is an enum in spec and implementation:
https://immersive-web.github.io/webxr/#xrsessionmode-enum
https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/renderer/modules/xr/xr_session.idl;l=7;drc=d78a26c4267a178f6ceefb599478692907cd6206

An enum is basically a subset of a string, where only certain strings are allowed and others cause TypeError to be thrown. So what it means for XRSessionMode is really for these strings to work as arguments for one of the two methods here:
https://immersive-web.github.io/webxr/#xrsystem-interface

If those methods aren't supported in WebView, then this enum can't be either.

Aside: I'm skeptical about having enums in BCD at all, but that's for #6810.

[queengooborg]

My mistake, I thought I had tested this in the collector as well. I've followed this up with #10926 to set this all to false.