Avoid using PATH to find dotnet.exe in RazorSDK tasks (#25750)

This pattern is pretty identical to what we have in other SDKs. It allows
using the SDK when dotnet isn't in the path such as the https://github.com/dotnet/aspnetcore/issues/25746.

Fixes #14432

src/Razor/Microsoft.NET.Sdk.Razor/src/DotnetToolTask.cs

@@ -10,7 +10,6 @@ using System.Threading;
 using Microsoft.AspNetCore.Razor.Tools;
 using Microsoft.Build.Framework;
 using Microsoft.Build.Utilities;
-using Microsoft.Extensions.CommandLineUtils;
 
 namespace Microsoft.AspNetCore.Razor.Tasks
 {
@@ -19,6 +18,7 @@ namespace Microsoft.AspNetCore.Razor.Tasks
         // From https://github.com/dotnet/corefx/blob/29cd6a0b0ac2993cee23ebaf36ca3d4bce6dd75f/src/System.IO.Pipes/ref/System.IO.Pipes.cs#L93.
         // Using the enum value directly as this option is not available in netstandard.
         private const PipeOptions PipeOptionCurrentUserOnly = (PipeOptions)536870912;
+        private string _dotnetPath;
 
         private CancellationTokenSource _razorServerCts;
 
@@ -40,7 +40,7 @@ namespace Microsoft.AspNetCore.Razor.Tasks
 
         public string PipeName { get; set; }
 
-        protected override string ToolName => "dotnet";
+        protected override string ToolName => Path.GetDirectoryName(DotNetPath);
 
         // If we're debugging then make all of the stdout gets logged in MSBuild
         protected override MessageImportance StandardOutputLoggingImportance => DebugTool ? MessageImportance.High : base.StandardOutputLoggingImportance;
@@ -49,17 +49,25 @@ namespace Microsoft.AspNetCore.Razor.Tasks
 
         internal abstract string Command { get; }
 
-        protected override string GenerateFullPathToTool()
-        {
-#if NETSTANDARD2_0
-            if (!string.IsNullOrEmpty(DotNetMuxer.MuxerPath))
-            {
-                return DotNetMuxer.MuxerPath;
-            }
-#endif
+        protected override string GenerateFullPathToTool() => DotNetPath;
 
-            // use PATH to find dotnet
-            return ToolExe;
+        private string DotNetPath
+        {
+            get
+            {
+                if (!string.IsNullOrEmpty(_dotnetPath))
+                {
+                    return _dotnetPath;
+                }
+
+                _dotnetPath = Environment.GetEnvironmentVariable("DOTNET_HOST_PATH");
+                if (string.IsNullOrEmpty(_dotnetPath))
+                {
+                    throw new InvalidOperationException("DOTNET_HOST_PATH is not set");
+                }
+
+                return _dotnetPath;
+            }
         }
 
         protected override string GenerateCommandLineCommands()

src/Razor/Microsoft.NET.Sdk.Razor/src/Microsoft.NET.Sdk.Razor.csproj

@@ -49,7 +49,7 @@
     <Compile Include="..\..\Microsoft.AspNetCore.Razor.Tools\src\Client.cs">
       <Link>Shared\Client.cs</Link>
     </Compile>
-    <Compile Include="$(SharedSourceRoot)CommandLineUtils\**\*.cs" />
+    <Compile Include="$(SharedSourceRoot)CommandLineUtils\Utilities\ArgumentEscaper.cs" />
 
     <Content Include="_._" CopyToOutputDirectory="PreserveNewest" />
   </ItemGroup>

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Microsoft.NET.Sdk.Razor.CodeGeneration.targets

@@ -98,6 +98,8 @@ Copyright (c) .NET Foundation. All rights reserved.
       Debug="$(_RazorDebugTagHelperTask)"
       DebugTool="$(_RazorDebugTagHelperTool)"
       ToolAssembly="$(_RazorSdkToolAssembly)"
+      ToolExe="$(_RazorSdkDotNetHostFileName)"
+      ToolPath="$(_RazorSdkDotNetHostDirectory)"
       UseServer="$(UseRazorBuildServer)"
       ForceServer="$(_RazorForceBuildServer)"
       PipeName="$(_RazorBuildServerPipeName)"
@@ -149,6 +151,8 @@ Copyright (c) .NET Foundation. All rights reserved.
       Debug="$(_RazorDebugGenerateCodeTask)"
       DebugTool="$(_RazorDebugGenerateCodeTool)"
       ToolAssembly="$(_RazorSdkToolAssembly)"
+      ToolExe="$(_RazorSdkDotNetHostFileName)"
+      ToolPath="$(_RazorSdkDotNetHostDirectory)"
       UseServer="$(UseRazorBuildServer)"
       ForceServer="$(_RazorForceBuildServer)"
       PipeName="$(_RazorBuildServerPipeName)"

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Microsoft.NET.Sdk.Razor.Component.targets

@@ -107,6 +107,8 @@ Copyright (c) .NET Foundation. All rights reserved.
     <RazorGenerate
       Debug="$(_RazorDebugGenerateCodeTask)"
       DebugTool="$(_RazorDebugGenerateCodeTool)"
+      ToolExe="$(_RazorSdkDotNetHostFileName)"
+      ToolPath="$(_RazorSdkDotNetHostDirectory)"
       ToolAssembly="$(_RazorSdkToolAssembly)"
       UseServer="$(UseRazorBuildServer)"
       ForceServer="$(_RazorForceBuildServer)"

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Microsoft.NET.Sdk.Razor.ScopedCss.targets

@@ -177,7 +177,9 @@ Integration with static web assets:
   <MakeDir Directories="$(_ScopedCssIntermediatePath)" />
   <RewriteCss
     FilesToTransform="@(_ScopedCss)"
-    ToolAssembly="$(_RazorSdkToolAssembly)">
+    ToolAssembly="$(_RazorSdkToolAssembly)"
+    ToolExe="$(_RazorSdkDotNetHostFileName)"
+    ToolPath="$(_RazorSdkDotNetHostDirectory)">
   </RewriteCss>
 
   <ItemGroup>

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Sdk.Razor.CurrentVersion.targets

@@ -36,6 +36,12 @@ Copyright (c) .NET Foundation. All rights reserved.
     <_RazorSdkToolAssembly>$(RazorSdkDirectoryRoot)tools\rzc.dll</_RazorSdkToolAssembly>
   </PropertyGroup>
 
+  <PropertyGroup Condition="'$(DOTNET_HOST_PATH)' == ''">
+    <_RazorSdkDotNetHostDirectory>$(NetCoreRoot)</_RazorSdkDotNetHostDirectory>
+    <_RazorSdkDotNetHostFileName>dotnet</_RazorSdkDotNetHostFileName>
+    <_RazorSdkDotNetHostFileName Condition="'$(OS)' == 'Windows_NT'">dotnet.exe</_RazorSdkDotNetHostFileName>
+  </PropertyGroup>
+
   <!-- Resolve the RazorLangVersion based on values imported or TFM. -->
   <PropertyGroup>
     <_TargetingNETCoreApp30OrLater Condition=" '$(TargetFrameworkIdentifier)' == '.NETCoreApp' AND