Setup event emitters for `TextShdowNode` and `ParagraphShadowNode`

Summary:
This diff includes two changes:
1. `TextShadowNode` represents virtual texts. For the time being, virtual text nodes only need touch capabilities so that they can handle `onPress` events for their children. Therefore, we should set the `TextShadowNode`'s `EventEmitterT` to `TouchEventEmitter`.
2. Since `ParagraphShadowNode` extends an instance of the `ConcreteViewShadowNode` template, it automatically uses the `ViewEventEmitter` if no event emitter is specified. I think it's better to make the event emitter explicitly specified. So, I've included that change in this diff.

Reviewed By: shergin

Differential Revision: D9696906

fbshipit-source-id: ac053ffdde4c2fbc6351f177c07a2ada4445cbb8

ReactCommon/fabric/components/text/paragraph/ParagraphShadowNode.h

@@ -21,6 +21,8 @@ namespace react {
 
 extern const char ParagraphComponentName[];
 
+using ParagraphEventEmitter = ViewEventEmitter;
+
 /*
  * `ShadowNode` for <Paragraph> component, represents <View>-like component
  * containing and displaying text. Text content is represented as nested <Text>
@@ -29,7 +31,8 @@ extern const char ParagraphComponentName[];
 class ParagraphShadowNode:
   public ConcreteViewShadowNode<
     ParagraphComponentName,
-    ParagraphProps
+    ParagraphProps,
+    ParagraphEventEmitter
   >,
   public BaseTextShadowNode {
 

ReactCommon/fabric/components/text/text/TextShadowNode.h

@@ -7,6 +7,7 @@
 
 #pragma once
 
+#include <fabric/components/view/ViewEventEmitter.h>
 #include <fabric/components/text/BaseTextShadowNode.h>
 #include <fabric/components/text/TextProps.h>
 #include <fabric/core/ConcreteShadowNode.h>
@@ -16,10 +17,13 @@ namespace react {
 
 extern const char TextComponentName[];
 
+using TextEventEmitter = TouchEventEmitter;
+
 class TextShadowNode:
   public ConcreteShadowNode<
     TextComponentName,
-    TextProps
+    TextProps,
+    TextEventEmitter
   >,
   public BaseTextShadowNode {