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/Multiline/RCTMultilineTextInputViewManager.m

@@ -9,25 +9,12 @@
 
 #import "RCTMultilineTextInputViewManager.h"
 
-#import <React/RCTBridge.h>
-#import <React/RCTConvert.h>
-#import <React/RCTFont.h>
-#import <React/RCTShadowView+Layout.h>
-#import <React/RCTShadowView.h>
-
-#import "RCTConvert+Text.h"
-#import "RCTMultilineTextInputShadowView.h"
 #import "RCTMultilineTextInputView.h"
 
 @implementation RCTMultilineTextInputViewManager
 
 RCT_EXPORT_MODULE()
 
-- (RCTShadowView *)shadowView
-{
-  return [RCTMultilineTextInputShadowView new];
-}
-
 - (UIView *)view
 {
   return [[RCTMultilineTextInputView alloc] initWithBridge:self.bridge];
@@ -35,12 +22,6 @@ RCT_EXPORT_MODULE()
 
 #pragma mark - Multiline <TextInput> (aka TextView) specific properties
 
-RCT_EXPORT_VIEW_PROPERTY(onChange, RCTBubblingEventBlock)
-RCT_EXPORT_VIEW_PROPERTY(onContentSizeChange, RCTBubblingEventBlock)
-RCT_EXPORT_VIEW_PROPERTY(onSelectionChange, RCTDirectEventBlock)
-RCT_EXPORT_VIEW_PROPERTY(onScroll, RCTDirectEventBlock)
-RCT_EXPORT_VIEW_PROPERTY(onTextInput, RCTDirectEventBlock)
-
 #if !TARGET_OS_TV
 RCT_REMAP_VIEW_PROPERTY(dataDetectorTypes, backedTextInputView.dataDetectorTypes, UIDataDetectorTypes)
 #endif