Android: cookie handling for proxied requests + avoid creating a new connection to check the contentType

[goapilz]

Fixes #2831
When using the "server.url" parameter in the capacitor.config.json to retrieve the app data from an external server incoming cookies are not saved to the CookieManager. Also an additional connection is opened in handleProxyRequest to check the contentType.

see: WebViewLocalServer:handleProxyRequest
see: JSInjector:getInjectedStream

My scenario:
Currently I use capacitor to add a native barcode scanner to my PWA app.
When running as simple PWA, the "browser camera api" is used, but when running in the capacitor app the native barcode scanner should be used.
Therefore capacitor seems to be the perfect framework.
But currently i have the described problem when the authentication cookie should be saved.

I would be happy if my change would be included in the project.

see issue:
#2831

[jcesarmobile]

Thanks for the PR
I've sent two separate PRs based on yours since they are 2 different problems and some changes weren't needed.
(#3078 and #3076)