Media Provider: Un-mark as internal so it can be optionally disabled

[nicjansma]

Alongside some Android startup improvements in #1089, I found that the Media processing was taking a long time during Pegasus startup.

For example, on an Anbernic RG405M device with 40k+ screenshots, it's taking over 32s:

2023-11-08T15:49:55 [i] Media: Finished searching in 32105ms

Guided by a comment in #839 (comment), I tried disabling the Media provider, and it cut out this delay entirely.

After I did this, I reviewed my theme and could not find any side-effects -- all screenshots were continuing to load OK. I reviewed its code, and could not find other obvious places its output would be used, so I must be missing something. Is there something the MediaProvider is doing that I'm breaking by disabling it?

Anyways, for my use-case, it seems like avoiding the MediaProvider is beneficial (faster startup) and causes no side-effects.

This PR un-marks the MediaProvider as internal, so that users can optionally disable it in via just the UI, instead of building a custom APK.

[mmatyas]

The Media provider looks for assets for your games, but based on the other issue, and that none of the provider are turned on on your screenshot, I assume all your games already have those set manually. It does sound reasonable to disable the Media provider in that case. Thank you for your contribution!

[mmatyas]

I was planning to update the provider name, but got a bit delayed... I'll just merge this first.