Removed dependency to Microsoft.Dotnet.Cli.Utils

[vlada-shubina]

Problem

• fixes Consider dropping dependency to Microsoft.DotNet.Cli.Utils. #5296

Solution

Created separated CommandUtils package usable from CLI and XUnit tests.
Removed dependency to Microsoft.Dotnet.Cli.Utils.

Checks:

• Added unit tests
• Added #nullable enable to all the modified files ?

[vlada-shubina]

@JanKrivanek I excluded the tools from source-build in the last commit. If they are needed, we can turn it on again.

[vlada-shubina]

we agreed not to create a public package at the time, and include the source code internally instead.

[vlada-shubina]

@JanKrivanek as agreed - moved the utils to shared internal code.
It might get too difficult to review - let me know if you'd like to split it into 2 PRs.

[JanKrivanek]

Overall looks good.
I have 2 minor things for considerations - but not strongly opinionated about those.

I'm very much looking forward for this to be merged!! :-) As it will simplify my life in unblocking dogfooding in sdk (need to be able to inject custom environemnt and dotnet assembly)

[vlada-shubina]

/backport to release/7.0.2xx

[github-actions]

Started backporting to release/7.0.2xx: https://github.com/dotnet/templating/actions/runs/3387467177

[github-actions]

@vlada-shubina backporting to release/7.0.2xx failed, the patch most likely resulted in conflicts:

$ git am --3way --ignore-whitespace --keep-non-patch changes.patch

Applying: removed dependency on Cli.Utils
Using index info to reconstruct a base tree...
M	eng/Versions.props
Falling back to patching base and 3-way merge...
Removing test/Microsoft.TemplateEngine.TestHelper/Commands/SdkCommandSpec.cs
Removing test/Microsoft.TemplateEngine.TestHelper/Commands/DotnetCommand.cs
Removing src/Microsoft.TemplateEngine.Authoring.TemplateVerifier/Commands/TestCommand.cs
Removing src/Microsoft.TemplateEngine.Authoring.TemplateVerifier/Commands/DotnetCommand.cs
Removing src/Microsoft.TemplateEngine.Authoring.TemplateVerifier/Commands/BasicCommand.cs
Auto-merging eng/Versions.props
CONFLICT (content): Merge conflict in eng/Versions.props
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 removed dependency on Cli.Utils
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".
Error: The process '/usr/bin/git' failed with exit code 128

Please backport manually!