--folder option is different in SDK bundled tool vs. mainline

Using the nightly (5 hours old) .NET SDK `6.0.100-rtm.21514.1` with bundled dotnet-format, `--folder` option doesn't have any effect.

```sh
$ dotnet6 format --version
6.0.251401+3ec0d2e1ffc98b76dca28aa23326ba0a1425dd82

# note that despite --folder, it is trying to load the workspace from csproj
$ ls *.cs | dotnet6 format --include - --folder -v:d
The dotnet runtime version is '6.0.0-rtm.21513.22'.
Formatting code files in workspace '/home/am11/projects/cs1/cs1.csproj'.
Determining projects to restore...
Restored /home/am11/projects/cs1/cs1.csproj (in 251 ms).
Project cs1 is using configuration from '/home/am11/projects/cs1/obj/Debug/net5.0/cs1.GeneratedMSBuildEditorConfig.editorconfig'.
Project cs1 is using configuration from '/home/am11/.dotnet6/sdk/6.0.100-rtm.21514.1/Sdks/Microsoft.NET.Sdk/analyzers/build/config/analysislevel_5_default.editorconfig'.
Running 1 analyzers on cs1.
Formatted 0 of 4 files.
Format complete in 10099ms.
```

with latest 5x (3 days old) downloaded from nuget.org, we get:
```sh
$ dotnet-format --version
5.1.250801+4a851ea9707f87d381166c2fc2b2d4b58a10a222

$ ls *.cs | dotnet-format --include - --folder -v:d
The dotnet format version is '5.1.250801+4a851ea9707f87d381166c2fc2b2d4b58a10a222'.
Formatting code files in workspace '/home/am11/projects/cs1'.
/home/am11/projects/cs1/Program.cs(1,1): error WHITESPACE: Fix whitespace formatting. [/home/am11/projects/cs1]
/home/am11/projects/cs1/Program2.cs(1,1): error WHITESPACE: Fix whitespace formatting. [/home/am11/projects/cs1]
Formatted code file '/home/am11/projects/cs1/Program.cs'.
Formatted code file '/home/am11/projects/cs1/Program2.cs'.
Formatted 2 of 2 files.
Format complete in 3514ms.
```
The expected behavior implemented by https://github.com/dotnet/format/pull/790.

Was it intentionally dropped out of .NET 6?