Clean up Razor Server pid file if the path doesn't exist

When the server path in the pid file didn't exist we'd hit an error:

```
The shutdown command failed: The application to execute does not exist
```

This can happen when the file wasn't cleaned up and the SDK was uninstalled in the meantime.
Ensure we delete the pid file in that case and don't error.

Fixes #10573

src/Cli/dotnet/BuildServer/RazorServer.cs

@@ -36,6 +36,14 @@ public RazorServer(
 
         public void Shutdown()
         {
+            if(!_fileSystem.File.Exists(PidFile.ServerPath.Value))
+            {
+                // The razor server path doesn't exist anymore so trying to shut it down would fail
+                // Ensure the pid file is cleaned up so we don't try to shut it down again
+                DeletePidFile();
+                return;
+            }
+
             var command = _commandFactory
                 .Create(
                     "exec",
@@ -60,6 +68,11 @@ public void Shutdown()
 
             // After a successful shutdown, ensure the pid file is deleted
             // If the pid file was left behind due to a rude exit, this ensures we don't try to shut it down again
+            DeletePidFile();
+        }
+
+        void DeletePidFile()
+        {
             try
             {
                 if (_fileSystem.File.Exists(PidFile.Path.Value))

src/Tests/dotnet.Tests/BuildServerTests/RazorServerTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using FluentAssertions;
@@ -31,14 +32,16 @@ public void GivenAFailedShutdownCommandItThrows()
             string pidDirectory = Path.GetFullPath("var/pids/build");
             string pidFilePath = Path.Combine(pidDirectory, $"{RazorPidFile.FilePrefix}{ProcessId}");
 
+            var serverPath = Path.GetFullPath("path/to/rzc.dll");
+
             var fileSystemMock = new FileSystemMockBuilder()
                 .AddFile(pidFilePath, "")
+                .AddFile(serverPath, "")
                 .UseCurrentSystemTemporaryDirectory()
                 .Build();
 
             fileSystemMock.File.Exists(pidFilePath).Should().BeTrue();
-
-            var serverPath = Path.Combine(fileSystemMock.Directory.CreateTemporaryDirectory().DirectoryPath, "path/to/rzc.dll");
+            fileSystemMock.File.Exists(serverPath).Should().BeTrue();
 
             var server = new RazorServer(
                 pidFile: new RazorPidFile(
@@ -68,14 +71,16 @@ public void GivenASuccessfulShutdownItDoesNotThrow()
             string pidDirectory = Path.GetFullPath("var/pids/build");
             string pidFilePath = Path.Combine(pidDirectory, $"{RazorPidFile.FilePrefix}{ProcessId}");
 
+            var serverPath = Path.GetFullPath("path/to/rzc.dll");
+
             var fileSystemMock = new FileSystemMockBuilder()
                 .AddFile(pidFilePath, "")
+                .AddFile(serverPath, "")
                 .UseCurrentSystemTemporaryDirectory()
                 .Build();
 
             fileSystemMock.File.Exists(pidFilePath).Should().BeTrue();
-
-            var serverPath = Path.Combine(fileSystemMock.Directory.CreateTemporaryDirectory().DirectoryPath, "path/to/rzc.dll");
+            fileSystemMock.File.Exists(serverPath).Should().BeTrue();
 
             var server = new RazorServer(
                 pidFile: new RazorPidFile(
@@ -91,6 +96,43 @@ public void GivenASuccessfulShutdownItDoesNotThrow()
             fileSystemMock.File.Exists(pidFilePath).Should().BeFalse();
         }
 
+        [Fact]
+        public void GivenANonExistingRazorServerPathItDeletesPidFileAndDoesNotThrow()
+        {
+            const int ProcessId = 1234;
+            const string PipeName = "some-pipe-name";
+
+            string pidDirectory = Path.GetFullPath("var/pids/build");
+            string pidFilePath = Path.Combine(pidDirectory, $"{RazorPidFile.FilePrefix}{ProcessId}");
+
+            var serverPath = Path.GetFullPath("path/to/rzc.dll");
+
+            var fileSystemMock = new FileSystemMockBuilder()
+                .AddFile(pidFilePath, "")
+                .UseCurrentSystemTemporaryDirectory()
+                .Build();
+
+            fileSystemMock.File.Exists(pidFilePath).Should().BeTrue();
+            fileSystemMock.File.Exists(serverPath).Should().BeFalse();
+
+            var commandFactoryMock = CreateCommandFactoryMock(serverPath, PipeName);
+            var server = new RazorServer(
+                pidFile: new RazorPidFile(
+                    path: new FilePath(pidFilePath),
+                    processId: ProcessId,
+                    serverPath: new FilePath(serverPath),
+                    pipeName: PipeName),
+                commandFactory: commandFactoryMock.Object,
+                fileSystem: fileSystemMock);
+
+            Action a = () => server.Shutdown();
+
+            a.Should().NotThrow();
+            commandFactoryMock.Verify(c => c.Create(It.IsAny<string>(), It.IsAny<IEnumerable<string>>(), It.IsAny<NuGetFramework>(), It.IsAny<string>()), Times.Never);
+
+            fileSystemMock.File.Exists(pidFilePath).Should().BeFalse();
+        }
+
         private Mock<ICommandFactory> CreateCommandFactoryMock(string serverPath, string pipeName, int exitCode = 0, string stdErr = "")
         {
             var commandMock = new Mock<ICommand>(MockBehavior.Strict);