Limit number of contacts for Android's "Quick Share"

[genodeftest]

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• I have read how to contribute to this project
• I have signed the Contributor License Agreement

Contributor checklist

• I am following the Code Style Guidelines
• I have tested my contribution on these devices:

• None, as I do not currently have a setup to build Signal for Android and no way to test it with real contact data

• My contribution is fully baked and ready to be merged as is
• I ensure that all the open issues my contribution fixes are mentioned in the commit message of my first commit using the Fixes #1234 syntax

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Description

Work around a bug in Android which leads to non recent conversations showing up in Android's "Quick Share" overlay instead of the most recent conversations. As a side effect, leak less conversation names to the Android OS.

Fixes #13398

Notes:

• The number 10 is arbitrarily chosen, as was the original number 150 if I understand commit 8783d15 correctly. On the Android UIs I have seen so far, there are only 4 or 5 "Quick Share" items to be displayed by the OS, but there may be other UIs. Feel free to adapt the number to whatever you think is more useful.
• I don't have access to a machine that is suitable for building and testing this change at the moment. Can someone else please test this change for me?