chore: use build-android/ios commands in added scripts inside example app (#569)

### Summary

With fairly new commands `build-android/ios` added inside React Native
Community CLI we can replace manually calling `./gradlew` and
`xcodebuild` inside `build:android` and `build:ios` scripts.

### Test plan

1. Generate new project with `create-react-native-library`
2. `build:android` and `build:ios` scripts should have the same result
as before ✅

Author: szymonrybczak

packages/create-react-native-library/src/utils/generateExampleApp.ts

@@ -109,8 +109,8 @@ export default async function generateExampleApp({
 
   const SCRIPTS_TO_ADD = {
     'build:android':
-      'cd android && ./gradlew assembleDebug --no-daemon --console=plain -PreactNativeArchitectures=arm64-v8a',
-    'build:ios': `cd ios && xcodebuild -workspace ${projectName}Example.xcworkspace -scheme ${projectName}Example -configuration Debug -sdk iphonesimulator CC=clang CPLUSPLUS=clang++ LD=clang LDPLUSPLUS=clang++ GCC_OPTIMIZATION_LEVEL=0 GCC_PRECOMPILE_PREFIX_HEADER=YES ASSETCATALOG_COMPILER_OPTIMIZATION=time DEBUG_INFORMATION_FORMAT=dwarf COMPILER_INDEX_STORE_ENABLE=NO`,
+      'react-native build-android --extra-params "--no-daemon --console=plain -PreactNativeArchitectures=arm64-v8a"',
+    'build:ios': `react-native build-ios --scheme ${projectName}Example --mode Debug --extra-params "-sdk iphonesimulator CC=clang CPLUSPLUS=clang++ LD=clang LDPLUSPLUS=clang++ GCC_OPTIMIZATION_LEVEL=0 GCC_PRECOMPILE_PREFIX_HEADER=YES ASSETCATALOG_COMPILER_OPTIMIZATION=time DEBUG_INFORMATION_FORMAT=dwarf COMPILER_INDEX_STORE_ENABLE=NO"`,
   };
 
   if (type === 'native') {