Moved build artifacts to build/

Directory.Build.props copied from
dotnet/msbuild#1603 (comment)

.gitignore

@@ -1,3 +1,6 @@
+## Build artifacts/
+build/
+
 ## Ignore Visual Studio temporary files, build results, and
 ## files generated by popular Visual Studio add-ons.
 ##

Directory.Build.props

@@ -0,0 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <!-- Common properties -->
+  <PropertyGroup>
+    <!-- SolutionDir is not defined when building projects explicitly -->
+    <SolutionDir Condition=" '$(SolutionDir)' == '' ">$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildProjectDirectory), Microsoft.MixedReality.Sharing.sln))\</SolutionDir>
+    <!-- Output paths -->
+    <BaseIntermediateOutputPath>$(SolutionDir)build\obj\$(Configuration)\$(MSBuildProjectName)\</BaseIntermediateOutputPath>
+    <IntermediateOutputPath>$(SolutionDir)build\obj\$(Configuration)\$(MSBuildProjectName)\</IntermediateOutputPath>
+    <MSBuildProjectExtensionsPath>$(IntermediateOutputPath)\</MSBuildProjectExtensionsPath>
+    <OutputPath>$(SolutionDir)build\out\$(Configuration)\</OutputPath>
+    <OutDir>$(OutputPath)</OutDir>
+  </PropertyGroup>
+</Project>

libs/Microsoft.MixedReality.Sharing.Network/Microsoft.MixedReality.Sharing.Network.csproj

@@ -4,12 +4,4 @@
     <TargetFramework>netstandard2.0</TargetFramework>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
-    <OutputPath></OutputPath>
-  </PropertyGroup>
-
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
-    <OutputPath></OutputPath>
-  </PropertyGroup>
-
 </Project>

libs/Microsoft.MixedReality.Sharing.StateSync/Microsoft.MixedReality.Sharing.StateSync.csproj

@@ -4,8 +4,4 @@
     <TargetFramework>netstandard2.0</TargetFramework>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|AnyCPU'">
-    <OutputPath></OutputPath>
-  </PropertyGroup>
-
 </Project>