<Text> module add textDecoration style attributes

Summary:
This is simply a rebased and squashed version of @KJlmfe's PR over at https://github.com/facebook/react-native/pull/845

It was actually already squashed into one commit, but for some reason that was hard to see from the original PR.
Closes https://github.com/facebook/react-native/pull/1869
Github Author: KJlmfe <kjlmfe@gmail.com>

React/Base/RCTConvert.h

@@ -12,10 +12,12 @@
 
 #import "Layout.h"
 #import "RCTAnimationType.h"
+#import "RCTTextDecorationLineType.h"
 #import "RCTDefines.h"
 #import "RCTLog.h"
 #import "RCTPointerEvents.h"
 
+
 /**
  * This class provides a collection of conversion functions for mapping
  * JSON objects to native types and classes. These are useful when writing
@@ -54,6 +56,7 @@ typedef NSURL RCTFileURL;
 + (NSTimeInterval)NSTimeInterval:(id)json;
 
 + (NSTextAlignment)NSTextAlignment:(id)json;
++ (NSUnderlineStyle)NSUnderlineStyle:(id)json;
 + (NSWritingDirection)NSWritingDirection:(id)json;
 + (UITextAutocapitalizationType)UITextAutocapitalizationType:(id)json;
 + (UITextFieldViewMode)UITextFieldViewMode:(id)json;
@@ -126,6 +129,7 @@ typedef BOOL css_clip_t;
 
 + (RCTPointerEvents)RCTPointerEvents:(id)json;
 + (RCTAnimationType)RCTAnimationType:(id)json;
++ (RCTTextDecorationLineType)RCTTextDecorationLineType:(id)json;
 
 @end
 

React/Base/RCTConvert.m

@@ -216,6 +216,20 @@ RCT_ENUM_CONVERTER(NSTextAlignment, (@{
   @"justify": @(NSTextAlignmentJustified),
 }), NSTextAlignmentNatural, integerValue)
 
+RCT_ENUM_CONVERTER(NSUnderlineStyle, (@{
+  @"solid": @(NSUnderlineStyleSingle),
+  @"double": @(NSUnderlineStyleDouble),
+  @"dotted": @(NSUnderlinePatternDot | NSUnderlineStyleSingle),
+  @"dashed": @(NSUnderlinePatternDash | NSUnderlineStyleSingle),
+}), NSUnderlineStyleSingle, integerValue)
+
+RCT_ENUM_CONVERTER(RCTTextDecorationLineType, (@{
+  @"none": @(RCTTextDecorationLineTypeNone),
+  @"underline": @(RCTTextDecorationLineTypeUnderline),
+  @"line-through": @(RCTTextDecorationLineTypeStrikethrough),
+  @"underline line-through": @(RCTTextDecorationLineTypeUnderlineStrikethrough),
+}), RCTTextDecorationLineTypeNone, integerValue)
+
 RCT_ENUM_CONVERTER(NSWritingDirection, (@{
   @"auto": @(NSWritingDirectionNatural),
   @"ltr": @(NSWritingDirectionLeftToRight),