[igotlinux]

First time contributor checklist

• I have tested my contribution on these devices:

• Android Emulator (Pixel, Android 14 / API 34), playDebug
• Android Physical Device, playDebug

• 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 (Fixes Low-res emojis #53)

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Description

Fixes #53

Note on #1053: I noticed #1053 previously attempted a larger emoji pipeline rewrite but has experienced merge conflicts on dev. This PR proposes a lightweight, non-breaking user preference toggle ("Use System Emojis") that immediately delivers crisp emojis on modern devices without requiring assets removal or breaking backward compatibility.

Session currently uses a legacy 66x66px bitmap spritesheet pipeline (EmojiProvider / EmojiTextView) inherited from older Signal code. On modern high-DPI screens, these small bitmap tiles appear blurry and pixelated when scaled up.

This PR adds a "Use System Emojis" toggle in Settings → Chats (enabled by default) that allows messages to render sharp, high-resolution vector emojis using the device's native emoji font rather than the low-resolution spritesheets.

Changes:

• Added USE_SYSTEM_EMOJI key and getter/setter preferences in TextSecurePreferences.kt (defaults to true).
• Updated EmojiTextView.java to check isUseSystemEmojiEnabled() before parsing/replacing emoji spans; when enabled, it skips the bitmap spritesheet replacement and renders the native Unicode characters.
• Added preference toggle in ChatsPreferenceScreen.kt and state handling in ChatsPreferenceViewModel.kt.

Testing:

• Verified in Android Studio with assemblePlayDebug and testPlayDebugUnitTest (all tests pass).
• Toggled on/off in Settings → Chats and verified emoji sharpness in conversation views.