Change default project name to UnitTestApp (#4775)

* Change default project name to UnitTestApp

Visual Studio team recommends

* Change default project name to UnitTestApp

Visual Studio team recommends

Author: Scottj1s

dev/VSIX/ProjectTemplates/Desktop/CSharp/UnitTestApp/WinUI.Desktop.Cs.UnitTestApp.vstemplate

@@ -8,7 +8,7 @@
     <TemplateGroupID>WinRT-Managed</TemplateGroupID>
     <ProjectType>CSharp</ProjectType>
     <CreateNewFolder>true</CreateNewFolder>
-    <DefaultName>App</DefaultName>
+    <DefaultName>UnitTestApp</DefaultName>
     <ProvideDefaultName>true</ProvideDefaultName>
     <LocationField>Enabled</LocationField>
     <EnableLocationBrowseButton>true</EnableLocationBrowseButton>

dev/VSIX/ProjectTemplates/Desktop/CppWinRT/UnitTestApp/WinUI.Desktop.CppWinRT.UnitTestApp.vstemplate

@@ -7,7 +7,7 @@
     <TemplateID>Microsoft.WinUI.Desktop.CppWinRT.UnitTestApp</TemplateID>
     <ProjectType>VC</ProjectType>
     <CreateNewFolder>true</CreateNewFolder>
-    <DefaultName>App</DefaultName>
+    <DefaultName>UnitTestApp</DefaultName>
     <ProvideDefaultName>true</ProvideDefaultName>
     <LocationField>Enabled</LocationField>
     <EnableLocationBrowseButton>true</EnableLocationBrowseButton>