Use C++17 namespace (#41771)

Summary:
Pull Request resolved: #41771

Changelog: [Internal]

Since we are already enforcing C++20 (and 17), we can set the namespace declaration to the C++17 style

Reviewed By: NickGerleman

Differential Revision: D51789991

fbshipit-source-id: 165d7d4e652d60ab200e2355e084010a02f470a4

packages/react-native-codegen/e2e/__tests__/modules/__snapshots__/GenerateModuleCpp-test.js.snap

@@ -12,8 +12,7 @@ exports[`GenerateModuleCpp can generate a header file NativeModule specs with as
 
 #include \\"RNCodegenModuleFixturesJSI.h\\"
 
-namespace facebook {
-namespace react {
+namespace facebook::react {
 
 static jsi::Value __hostFunction_NativeArrayTurboModuleCxxSpecJSI_getArray(jsi::Runtime &rt, TurboModule &turboModule, const jsi::Value* args, size_t count) {
   return static_cast<NativeArrayTurboModuleCxxSpecJSI *>(&turboModule)->getArray(
@@ -818,8 +817,7 @@ NativeStringTurboModuleCxxSpecJSI::NativeStringTurboModuleCxxSpecJSI(std::shared
 }
 
 
-} // namespace react
-} // namespace facebook
+} // namespace facebook::react
 "
 `;
 
@@ -835,8 +833,7 @@ exports[`GenerateModuleCpp can generate an implementation file NativeModule spec
 
 #include \\"RNCodegenModuleFixturesJSI.h\\"
 
-namespace facebook {
-namespace react {
+namespace facebook::react {
 
 static jsi::Value __hostFunction_NativeArrayTurboModuleCxxSpecJSI_getArray(jsi::Runtime &rt, TurboModule &turboModule, const jsi::Value* args, size_t count) {
   return static_cast<NativeArrayTurboModuleCxxSpecJSI *>(&turboModule)->getArray(
@@ -1641,7 +1638,6 @@ NativeStringTurboModuleCxxSpecJSI::NativeStringTurboModuleCxxSpecJSI(std::shared
 }
 
 
-} // namespace react
-} // namespace facebook
+} // namespace facebook::react
 "
 `;

packages/react-native-codegen/e2e/__tests__/modules/__snapshots__/GenerateModuleH-test.js.snap

@@ -15,8 +15,7 @@ exports[`GenerateModuleH can generate a header file NativeModule specs 1`] = `
 #include <ReactCommon/TurboModule.h>
 #include <react/bridging/Bridging.h>
 
-namespace facebook {
-namespace react {
+namespace facebook::react {
 
 
   class JSI_EXPORT NativeArrayTurboModuleCxxSpecJSI : public TurboModule {
@@ -2345,8 +2344,7 @@ private:
   Delegate delegate_;
 };
 
-} // namespace react
-} // namespace facebook
+} // namespace facebook::react
 "
 `;
 
@@ -2365,8 +2363,7 @@ exports[`GenerateModuleH can generate a header file NativeModule specs with assu
 #include <ReactCommon/TurboModule.h>
 #include <react/bridging/Bridging.h>
 
-namespace facebook {
-namespace react {
+namespace facebook::react {
 
 
   class JSI_EXPORT NativeArrayTurboModuleCxxSpecJSI : public TurboModule {
@@ -4695,7 +4692,6 @@ private:
   Delegate delegate_;
 };
 
-} // namespace react
-} // namespace facebook
+} // namespace facebook::react
 "
 `;