Improve JS injection method

[CarlosOlivo]

No more undefined NativeShell

Before

V/WebView: ApiClient serverAddress: http://10.0.2.2:8096, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js (2)
V/WebView: ApiClient appName: undefined, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js (2)
V/WebView: ApiClient appVersion: undefined, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js (2)
V/WebView: ApiClient deviceName: undefined, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js (2)
V/WebView: ApiClient deviceId: undefined, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js (2)

After

V/WebView: ApiClient serverAddress: http://10.0.2.2:8096, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js?1623960060466 (2)
V/WebView: ApiClient appName: Jellyfin Android, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js?1623960060466 (2)
V/WebView: ApiClient appVersion: 0.0.0-dev.1, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js?1623960060466 (2)
V/WebView: ApiClient deviceName: sdk_gphone_x86, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js?1623960060466 (2)
V/WebView: ApiClient deviceId: 9c17977ed5b293fb, http://10.0.2.2:8096/web/main.4b4b736dbefe7c3a90ec.bundle.js?1623960060466 (2)

[Maxr1998]

Looks good! I will do some more on-device testing tomorrow and merge it if I don't find any side-effects.

[CarlosOlivo]

I found that WebViewAssetLoader.AssetsPathHandler exists, so I removed WebAppUtils.kt

[CarlosOlivo]

See #439 (comment) I think it is better than running a regex comparison for each request.