Revert to test projects created in bindir, instead of a temp one

This was necessary because on windows the tmp path is very long, causing
the test project paths to become too long causing build failures.

src/mono/wasm/Wasm.Build.Tests/BuildEnvironment.cs

@@ -27,7 +27,7 @@ public class BuildEnvironment
         public static readonly string           RelativeTestAssetsPath = @"..\testassets\";
         public static readonly string           TestAssetsPath = Path.Combine(AppContext.BaseDirectory, "testassets");
         public static readonly string           TestDataPath = Path.Combine(AppContext.BaseDirectory, "data");
-        public static readonly string           TmpPath = Path.Combine(Path.GetTempPath(), "wasmbuildtests");
+        public static readonly string           TmpPath = Path.Combine(AppContext.BaseDirectory, "wbt");
 
         private static readonly Dictionary<string, string> s_runtimePackVersions = new();
 

src/mono/wasm/Wasm.Build.Tests/BuildTestBase.cs

@@ -281,7 +281,7 @@ public BuildTestBase(ITestOutputHelper output, SharedBuildPerTestClassFixture bu
         protected void InitPaths(string id)
         {
             if (_projectDir == null)
-                _projectDir = Path.Combine(AppContext.BaseDirectory, id);
+                _projectDir = Path.Combine(BuildEnvironment.TmpPath, id);
             _logPath = Path.Combine(s_buildEnv.LogRootPath, id);
             _nugetPackagesDir = Path.Combine(BuildEnvironment.TmpPath, "nuget", id);
 
@@ -466,7 +466,7 @@ private static string GetNuGetConfigWithLocalPackagesPath(string templatePath, s
         public string CreateWasmTemplateProject(string id, string template = "wasmbrowser", string extraArgs = "")
         {
             InitPaths(id);
-            InitProjectDir(id, addNuGetSourceForLocalPackages: true);
+            InitProjectDir(_projectDir, addNuGetSourceForLocalPackages: true);
 
             File.WriteAllText(Path.Combine(_projectDir, "Directory.Build.props"), "<Project />");
             File.WriteAllText(Path.Combine(_projectDir, "Directory.Build.targets"),