Wrong height when TextInput has an empty string

Summary:
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The caret/cursor did not appear when the TextInput was empty. Found that the cause was because the frame of the TextInput had an height of 0

Just fill and clear a TextInput and the caret/cursor will always appear there.

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  CATEGORY
[----------]        TYPE
[ CLI      ]   [-------------]      LOCATION
[ DOCS     ]   [ BREAKING    ]   [-------------]
[ GENERAL  ]   [ BUGFIX      ]   [-{Component}-]
[ INTERNAL ]   [ ENHANCEMENT ]   [ {File}      ]
[ IOS      ]   [ FEATURE     ]   [ {Directory} ]   |-----------|
[ ANDROID  ]   [ MINOR       ]   [ {Framework} ] - | {Message} |
[----------]   [-------------]   [-------------]   |-----------|

[CATEGORY] [TYPE] [LOCATION] - MESSAGE

 EXAMPLES:

 [IOS] [BREAKING] [FlatList] - Change a thing that breaks other things
 [ANDROID] [BUGFIX] [TextInput] - Did a thing to TextInput
 [CLI] [FEATURE] [local-cli/info/info.js] - CLI easier to do things with
 [DOCS] [BUGFIX] [GettingStarted.md] - Accidentally a thing/word
 [GENERAL] [ENHANCEMENT] [Yoga] - Added new yoga thing/position
 [INTERNAL] [FEATURE] [./scripts] - Added thing to script that nobody will see
-->
[IOS] [BUGFIX] [TextInput] - This was causing the cursor/caret to not appear since the size of the frame had an height of 0.
Closes https://github.com/facebook/react-native/pull/18355

Differential Revision: D7319723

Pulled By: shergin

fbshipit-source-id: b0249ab5493b6ac310d1898ff20c0bad78cf82c9

Libraries/Text/TextInput/RCTBaseTextInputShadowView.m

@@ -180,8 +180,8 @@
     // Placeholder also can represent the intrinsic size when it is visible.
     NSString *text = self.placeholder;
     if (!text.length) {
-      // Zero-width space
-      text = @"\u200B";
+      // Note: `zero-width space` is insufficient in some cases.
+      text = @"I";
     }
     attributedText = [[NSAttributedString alloc] initWithString:text attributes:self.textAttributes.effectiveTextAttributes];
   }