fix(android): allow compilation in old cordova-android versions

[jcesarmobile]

since the plugin don't have engines for cordova-android, people is using it in old cordova-android versions and it fails to compile because it uses some code that is not supported in older SDK compile versions.

This PR should make it compile in older versions (tested only 6.2.3 which targets android-25, could still fail in even older versions)

closes #554

after this is merged we should do a patch/minor release and then we can revert and set the engines to cordova-android 9 and remove a lot of code that wouldn't be needed, and then do a major release as updating the engines is a breaking change

[breautek]

I'm assuming this will cause breakage if running on later android targets. We should probably attempt to get this patch and the new major released around the same time.

[jcesarmobile]

no, it should still work on any capacitor-android version, even on newer ones, it just replaces constants which might not exist with the number they represent
and this other change https://github.com/apache/cordova-plugin-inappbrowser/pull/803/files#diff-b73be6c976a963c35af9c94c6c85447ca3fa5a70f417912f71cce92b16896874L272-L277 just removes getWebViewClient usage, which is not available if you compile on cordova-android 6.2.3 (SDK 25) or older, but the code does the same thing.

[timbru31]

Not really a big fan of introducing magic numbers, the Android constants exists for a reason and make reading the code a lot easier.

[jcesarmobile]

Yeah, this is a temporary fix, will revert it once released