Add TextInput's prop caretHidden implementation for Android and add the prop to docs

Summary:
This PR will:
- add missing documentation for `caretHidden` prop to the docs
- add `caretHidden` prop implementation for Android

I noticed this by accident when looking at `RCTTextFieldManager.m` and there is `RCT_EXPORT_VIEW_PROPERTY(caretHidden, BOOL)` which hides caret on iOS. Then I realised that the docs were missing for this prop and implementation on Android side :)

Render `TextInput` with prop `caretHidden`. After this caret is not visible anymore.
`<TextInput style={styles.input} caretHidden />`

If you omit the prop then caret is visible again
`<TextInput style={styles.input} />`
Closes https://github.com/facebook/react-native/pull/11863

Differential Revision: D4448402

fbshipit-source-id: 456e1df3e2cbb8af32540d2c7a8f4e7da219f5c3

ReactAndroid/src/main/java/com/facebook/react/views/textinput/ReactTextInputManager.java

@@ -346,6 +346,11 @@ public class ReactTextInputManager extends BaseViewManager<ReactEditText, Layout
     } catch (IllegalAccessException ex) {}
   }
 
+  @ReactProp(name = "caretHidden", defaultBoolean = false)
+  public void setCaretHidden(ReactEditText view, boolean caretHidden) {
+    view.setCursorVisible(!caretHidden);
+  }
+
   @ReactProp(name = "selectTextOnFocus", defaultBoolean = false)
   public void setSelectTextOnFocus(ReactEditText view, boolean selectTextOnFocus) {
     view.setSelectAllOnFocus(selectTextOnFocus);