Use platform specific default value for separator

[IllusionMH]

This PR fixes #128345

This PR naively sets explicit default value that should match current behavior on Windows.

P.S. @bpasero I tried to use Copy Relative Path in web version (lauched as yarn web as I don't have access to Codespaces), however it always copies with \\ independently from setting. Is it expected behavior or I should file new issue for web version?

[bpasero]

@IllusionMH we cannot set a default that is platform specific because a windows box might be connected to a linux remote. We only know the standard path separator at the time we copy the path by checking the remote OS.

[IllusionMH]

@bpasero agree. Looks like I've missed that VS Code correctly copies path on Windows when connected to WSL or Remote now so platform specific check doesn't make sense.

What about question about yarn web where it always copies e.g. \sample-folder\large\rnd.foo for both Copy Path and Copy Relative Path and doesn't account for "explorer.copyRelativePathSeparator": "/" at all? It is expected behavior?

[bpasero]

@IllusionMH good catch, looks like we fail to use the separator if we cannot find a formatting:

vscode/src/vs/workbench/services/label/common/labelService.ts

Lines 141 to 144 in 4153751

	if (formatting && options.separator) {
	// mixin separator if defined from the outside
	formatting = { ...formatting, separator: options.separator };
	}

Do you want to change this PR to fix that particular issue?

As to why we use backslash by default in web on Windows, I refer to @isidorn who owns the label service.

[isidorn]

backslash by default in web on Windows

I think we just use backslash by default on Windows. We did not write code for the web specific scenario.
But I think it might make sense if the use is copying paths from web to his local windows machine.

[IllusionMH]

copying paths from web to his local windows machine

@isidorn What are current expected workflows for "web" version? My assumption was that "web" version is mainly for Codespaces that connects to Linux under the hood and has self sufficient development environments/workflows that won't need local PC and local paths.
Is it wrong assumption?

@bpasero I can take a stab on it or at least will create separate issue to track this unexpected behavior for "web" builds and will close this PR as you already properly fixed #128345 .

[bpasero]

Sounds good thanks.