The New <Text> on iOS

Summary:
This is a complete rewrite of RCTText, the part of React Native which manages Text and TextInput components.

Key points:

* It's understandable now. It follows a simple architectural pattern, and it's easy to debug and iterate. Text flow layout is a first-class citizen in React Native layout system now, not just a wired special case. It also brings entirely new possibilities such as nested interleaving <Text> and <View> components.
* All <Text>-specific APIs were removed from UIManager and co (it's about ~16 public methods which were used exclusively only by <Text>).
* It relies on new Yoga measurement/cloning API and on-dirty handler. So, it removes built-in dirty propagation subsystem from RN completely.
* It caches string fragments properly and granularly on a per-node basis which makes updating text-containing components more performant.
* It does not instantiate UIView for virtual components which reduces memory utilization.
* It drastically improves <TextInput> capabilities (e.g. rich text inside single line <TextInput> is now supported).

Screenshots:
https://cl.ly/2j3r1V0L0324
https://cl.ly/3N2V3C3d3q3R

Reviewed By: mmmulani

Differential Revision: D6617326

fbshipit-source-id: 35d4d81b35c9870e9557d0211c0e934e6072a41e

Libraries/Text/TextInput/Singleline/RCTSinglelineTextInputViewManager.m

@@ -9,15 +9,8 @@
 
 #import "RCTSinglelineTextInputViewManager.h"
 
-#import <React/RCTBridge.h>
-#import <React/RCTFont.h>
-#import <React/RCTShadowView+Layout.h>
-#import <React/RCTShadowView.h>
-
-#import "RCTConvert+Text.h"
-#import "RCTSinglelineTextInputShadowView.h"
+#import "RCTBaseTextInputShadowView.h"
 #import "RCTSinglelineTextInputView.h"
-#import "RCTUITextField.h"
 
 @implementation RCTSinglelineTextInputViewManager
 
@@ -25,7 +18,12 @@ RCT_EXPORT_MODULE()
 
 - (RCTShadowView *)shadowView
 {
-  return [RCTSinglelineTextInputShadowView new];
+  RCTBaseTextInputShadowView *shadowView =
+    (RCTBaseTextInputShadowView *)[super shadowView];
+
+  shadowView.maximumNumberOfLines = 1;
+
+  return shadowView;
 }
 
 - (UIView *)view
@@ -33,10 +31,4 @@ RCT_EXPORT_MODULE()
   return [[RCTSinglelineTextInputView alloc] initWithBridge:self.bridge];
 }
 
-#pragma mark - Singleline <TextInput> (aka TextField) specific properties
-
-RCT_REMAP_VIEW_PROPERTY(caretHidden, backedTextInputView.caretHidden, BOOL)
-RCT_REMAP_VIEW_PROPERTY(clearButtonMode, backedTextInputView.clearButtonMode, UITextFieldViewMode)
-RCT_EXPORT_VIEW_PROPERTY(onSelectionChange, RCTDirectEventBlock)
-
 @end