Fabric Tests: Change null ShadowNode creation in StateReconciliationTest

[empyrical]

Summary

In StateReconciliationTest, the way initializer lists are used to create null ShadowNodes causes this error on Visual Studio 2017 on Windows:

auto result = (ShadowNode const *){nullptr};

---

StateReconciliationTest.cpp(35): error C4576: a parenthesized type followed by an init 
ializer list is a non-standard explicit type conversion syntax

This change allows this test to compile in Visual Studio 2017, and the effected tests successfully compile and pass on Windows. They also compile and pass on Linux and macOS (both built with Clang)

Changelog

[Internal] [Changed] - Fabric Tests: Change null ShadowNode creation in StateReconciliationTest

Test Plan

The Fabric test suite passes on Windows after this change is made. I also tested it under macOS and Linux built with Clang and they both pass with this change made.

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	7,209,453	32
android	hermes	armeabi-v7a	6,858,625	32
android	hermes	x86	7,644,089	20
android	hermes	x86_64	7,535,033	24
android	jsc	arm64-v8a	9,369,050	-8
android	jsc	armeabi-v7a	9,010,350	-12
android	jsc	x86	9,231,770	-12
android	jsc	x86_64	9,808,922	4

Base commit: 7e89934

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	n/a	--

Base commit: 7e89934

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
ios	-	universal	n/a	--

Base commit: 7e89934

[facebook-github-bot]

@shergin has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @empyrical in eafa49d.

^{When will my fix make it into a release? | Upcoming Releases}