Reuse cache even if key system type given in API is not the same

Thanks to the PR #1478, that basically allows integration tests on our
DRM logic without a real encrypted or decodable contents nor MSE/EME
available, I noticed that I very recently brought a minor regression in
the rewrite of the `MediaKeySystemAccess` cache reusage rules.

We relied on the `keySystems[].type` API to see if the cached one was
compatible to the new wanted one, we probably wanted to compare the
former with the `type` actually provided as argument to the
`navigator.requestMediaKeySystemAccess` API instead (e.g.
`keySystems[].type` could be set just to `widevine`, in which case the
RxPlayer will probably ask for `com.widevine.alpha` instead).

Thankfully, EME defines a
[`MediaKeySystemAccess.prototype.keySystem`](https://www.w3.org/TR/encrypted-media-2/#dom-navigator-requestmediakeysystemaccess)
property that seems to (according to that recommendation) always be equal
to the asked `keySystem`.

src/main_thread/decrypt/find_key_system.ts

@@ -478,7 +478,7 @@ export default function getMediaKeySystemAccess(
         currentState !== null &&
         !shouldRenewMediaKeySystemAccess() &&
         // TODO: Do it with MediaKeySystemAccess.prototype.keySystem instead?
-        keyType === currentState.keySystemOptions.type &&
+        keyType === currentState.mediaKeySystemAccess.keySystem &&
         eme.implementation === currentState.emeImplementation.implementation &&
         isNewMediaKeySystemConfigurationCompatibleWithPreviousOne(
           keySystemConfiguration,