Upgrade SoLoader to 0.10.4

[gnprice]

RN on Android relies on a Java library from Facebook called SoLoader, aka com.facebook.soloader:soloader.

We're currently using version 0.10.3. Previous history:
0fb4de6
fbe33a4

The actual version we're using can be verified by running tools/gradle :app:dependencies, and looking for lines like:

+--- com.facebook.soloader:soloader:{strictly 0.10.3} -> 0.10.3 (c)

When we uploaded v27.231 to Google Play, we got a warning that we're using an old buggy version of SoLoader. The warning pointed to this page:
https://support.google.com/googleplay/android-developer/answer/12576726
which in particular recommends upgrading to 0.10.4 or later. So we should do that.

There are a couple of newer versions, namely 0.10.5 and 0.11.0 (plus a couple of "pre-release" versions after that):
https://github.com/facebook/SoLoader/releases
But the description of 0.10.5 sounds higher-risk, and doesn't clearly identify what it improves:

Use system linker by default on Android N and above devices.

and the description of 0.11.0 sounds like a broad sweeping change.

So given that this app is in maintenance mode and we're trying to minimize the time we spend on it (in favor of finishing and launching the new app as early as possible), we'll stick with the conservative upgrade: just 0.10.4, which seems focused on bug fixes.