snapshotTextInputTextOnTextChanged

When true, TextInputComponentSpec.EditTextWithEventHandlers.onTextChanged stores a detached SpannableStringBuilder snapshot in savedText instead of the live buffer owned by the underlying EditText. This eliminates a TOCTOU race that crashes with IndexOutOfBoundsException in TextInputComponentSpec.createAndMeasureEditText when the layout thread reads the live buffer while the user concurrently mutates it on the main thread.