refactor: use project identifier instead of generic (#501)

### Summary

Doesn't really fix/improve anything, just a nitpick. `cpp` seems too
generic. Just close if it's not a welcome change. Thanks!

### Test plan

```
yarn example android
```

Author: dcangulo

packages/create-react-native-library/templates/cpp-library/android/CMakeLists.txt

@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 3.4.1)
 set (CMAKE_VERBOSE_MAKEFILE ON)
 set (CMAKE_CXX_STANDARD 11)
 
-add_library(cpp
+add_library(<%- project.identifier -%>
             SHARED
             ../cpp/<%- project.identifier -%>.cpp
             cpp-adapter.cpp

packages/create-react-native-library/templates/java-library-legacy/android/src/main/java/com/{%- project.package_dir %}/{%- project.name %}Module.java

@@ -24,7 +24,7 @@ public String getName() {
 
 <% if (project.cpp) { -%>
   static {
-    System.loadLibrary("cpp");
+    System.loadLibrary("<%- project.identifier -%>");
   }
 
   private static native double nativeMultiply(double a, double b);

packages/create-react-native-library/templates/java-library-mixed/android/src/main/java/com/{%- project.package_dir %}/{%- project.name %}Module.java

@@ -21,7 +21,7 @@ public String getName() {
 
 <% if (project.cpp) { -%>
   static {
-    System.loadLibrary("cpp");
+    System.loadLibrary("<%- project.identifier -%>");
   }
 
   public static native double nativeMultiply(double a, double b);

packages/create-react-native-library/templates/java-library-new/android/src/main/java/com/{%- project.package_dir %}/{%- project.name %}Module.java

@@ -21,7 +21,7 @@ public String getName() {
 
 <% if (project.cpp) { -%>
   static {
-    System.loadLibrary("cpp");
+    System.loadLibrary("<%- project.identifier -%>");
   }
 
   private static native double nativeMultiply(double a, double b);