feat: provide "proof of life" when downloading apk bundles

[TheTrueColonel]

Feature description

Currently when trying to download/patch apk bundles, for example reddit, the download throbber just spins without any sign that anything is even being done. This makes it very easy for people to assume it's not downloading or doing anything at all as it looks no different than if something is frozen.

Motivation

The importance of this is primarily, better UX, and reduced cases of people saying "bundles don't work" "reddit won't download" on the discord.

Acknowledgements

• I have checked all open and closed feature requests and this is not a duplicate
• I have chosen an appropriate title.
• All requested information has been provided properly.
• The feature request is only related to ReVanced Manager.

[Alluseri]

The irony is that in my case, the app isn't even capable of patching apkm bundles. It's greyed out in the normal file picker and if I force select it through Total Commander it says it failed to load the apk. "apkm" is what is provided on APKMirror. So whenever it tries pulling something from APKMirror, it gets stuck because it's not actually doing anything.

[Alluseri]

To add on what I said above. I tried patching a regular apk file and it actually worked! I used the built-in webview to navigate around APKMirror and download the file, and the patcher actually showed the download progress. So this feature, in principle, already exists. There is just no proper handling for erroneous cases (like downloading a bundle instead of a single apk, which is apparently not supported).