fix(mobile): follow the Android composer caret while typing

[egefeyzioglu]

Problem

On Android, once the chat composer reaches its max height it stops following the caret. Typing a long prompt leaves the current line out of view, and the user has to scroll the input by hand. Reported in #12690 on Samsung One UI devices and with physical keyboards.

Fix

The native editor now scrolls its own content so the caret line stays inside the viewport. SelectionAwareEditText computes the caret line from the text layout and adjusts scrollY when that line falls outside the padded viewport. It runs after text changes, selection changes, layout changes, controlled setSelection calls from JS, and when scrolling is enabled. scrollTo is a no-op while the composer is collapsed so the pill never jumps.

Fixes #12690

Evidence

I could not reproduce the bug on a Pixel 7 API 36 emulator with Gboard. Stock EditText already follows the caret there, on upstream main. The reports are from Samsung One UI and physical keyboards, so this still needs a check on a real device before merging.

• Before, on a Galaxy S25 Ultra, from the issue: https://github.com/user-attachments/assets/587525c8-0e97-4e7a-af99-f4d391b3a813
• Emulator, upstream main (no bug reproduced): video
• Emulator, this branch (same behaviour, no regression): video

upstream main (emulator)	this branch (emulator)

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