dotnet.py: --output is no longer supported with dotnet build/publish

.. with .sln files. Instead, pass `/p:PublishDir=..` to the build
command.

This changed in dotnet/sdk#29065, and broke
`dotnet-runtime-perf` pipeline's blazor scenarios.

```
$ dotnet publish /home/helixbot/work/A8850905/p/performance/src/scenarios/blazorpizza/app/BlazingPizza.sln --configuration Release --output pub /p:NuGetPackageRoot=/home/helixbot/work/A8850905/w/A9A608EA/u/artifacts/packages/ /p:UseSharedCompilation=false /p:BuildInParallel=false /m:1 --framework net7.0 /p:_TrimmerDumpDependencies=true -bl:./traces/blazor_publish.binlog -p:WasmNativeWorkload=false
MSBuild version 17.5.0-preview-22601-03+a2490dd3f for .NET

/home/helixbot/work/A8850905/p/dotnet/sdk/8.0.100-alpha.1.22606.3/Current/SolutionFile/ImportAfter/Microsoft.NET.Sdk.Solution.targets(36,5):
    error NETSDK1194: The "--output" option isn't supported when building a solution. [/home/helixbot/work/A8850905/p/performance/src/scenarios/blazorpizza/app/BlazingPizza.sln]
```

scripts/dotnet.py

@@ -338,7 +338,7 @@ def build(self,
             ]
 
             if output_to_bindir:
-                cmdline = cmdline + ['--output', self.__bin_directory]
+                cmdline += self.__get_output_build_arg(self.__bin_directory)
 
             if runtime_identifier:
                 cmdline = cmdline + ['--runtime', runtime_identifier]
@@ -362,7 +362,7 @@ def build(self,
                 ]
 
                 if output_to_bindir:
-                    cmdline = cmdline + ['--output', self.__bin_directory]
+                    cmdline += self.__get_output_build_arg(self.__bin_directory)
 
                 if runtime_identifier:
                     cmdline = cmdline + ['--runtime', runtime_identifier]
@@ -436,10 +436,10 @@ def publish(self,
             'dotnet', 'publish',
             self.csproj_file,
             '--configuration', configuration,
-            '--output', output_dir,
             "/p:NuGetPackageRoot={}".format(packages_path),
             '/p:UseSharedCompilation=false', '/p:BuildInParallel=false', '/m:1'
         ]
+        cmdline += self.__get_output_build_arg(output_dir)
         if runtime_identifier:
             cmdline += ['--runtime', runtime_identifier]
 
@@ -456,6 +456,13 @@ def publish(self,
             self.working_directory
         )
 
+    def __get_output_build_arg(self, outdir) -> list:
+        # dotnet build/publish does not support `--output` with sln files
+        if path.splitext(self.csproj_file)[1] == '.sln'
+            return ['/p:PublishDir=' + outdir]
+        else:
+            return ['--output', outdir]
+
     @staticmethod
     def __print_complus_environment() -> None:
         getLogger().info('-' * 50)