fix: report correct selection in Android onChange event during autofill

[nsbarsukov]

Summary:

On Android, filling a TextInput via platform autofill emits an onChange event whose nativeEvent.selection is {start: 0, end: 0} regardless of the inserted text length, while the same value inserted by pasting (and both paste and autofill on iOS) correctly reports the selection at the end of the inserted text.

The root cause is in the Android framework's autofill flow: TextView.autofill() first calls setText(), which notifies the TextWatchers — where ReactTextInputTextWatcher reads the selection for the topChange event — while the cursor still sits at its pre-autofill position, and only afterwards moves the cursor to the end of the new text. Paste is unaffected because clipboard insertion goes through Editable.replace(), which repositions the cursor before the watchers run.

This change tracks the in-progress autofill on ReactEditText (via an autofill() override setting an isBeingAutofilled flag) and, while it is set, reports the selection at the end of the new text — matching where the framework places the cursor immediately after.

Fixes #57458

Changelog:

[ANDROID] [FIXED] - TextInput onChange event reports stale selection ({start: 0, end: 0}) when text is inserted via platform autofill

Test Plan:

Added ReactTextInputTextWatcherTest (Robolectric), which drives the real framework View.autofill() path and asserts on the dispatched ReactTextChangedEvent payload:

• testAutofillReportsSelectionAtEndOfText — autofills +15551234567 and asserts the event carries text: "+15551234567" and selection: {start: 12, end: 12}. Without the fix this test fails with selection: {start: 0, end: 0}, reproducing the exact bug from the issue.
• testTextInsertedAtCursorReportsSelectionAfterInsertedText — regression-guards the paste/typing path (insertion at the cursor via Editable.insert()), which was already correct.

./gradlew :packages:react-native:ReactAndroid:testDebugUnitTest --tests "com.facebook.react.views.textinput.*"

ReactTextInputTextWatcherTest > testAutofillReportsSelectionAtEndOfText PASSED
ReactTextInputTextWatcherTest > testTextInsertedAtCursorReportsSelectionAfterInsertedText PASSED
ReactTextInputPropertyTest > (23 tests) PASSED

BUILD SUCCESSFUL