[RNMobile] Ensure dictating text doesn't cause cursor to be offset on…

… iOS (#51528)

The changes in this PR ensure that the cursor's position is always correct during dictation on iOS.

packages/react-native-aztec/ios/RNTAztecView/RCTAztecView.swift

@@ -356,8 +356,10 @@ class RCTAztecView: Aztec.TextView {
 
         // Replace occurrences of the obj symbol ("\u{FFFC}")
         textView.text = textView.text?.replacingOccurrences(of: "\u{FFFC}", with: "")
-
-        if let newPosition = textView.position(from: textView.beginningOfDocument, offset: originalPosition) {
+
+        // Detect if cursor is off-by-one and correct, if so
+        let newPositionOffset = originalPosition > 0 ? originalPosition - 1 : originalPosition
+        if let newPosition = textView.position(from: textView.beginningOfDocument, offset: newPositionOffset) {
             // Move the cursor to the correct, new position following dictation
             textView.selectedTextRange = textView.textRange(from: newPosition, to: newPosition)
         }