Should Environment.GetEnvironmentVariables return case-insensitive collection on Windows?

[adamsitnik]

As pointed by @stephentoub in #124271 (comment):

var d = Environment.GetEnvironmentVariables();
d.Clear();
d.Add("s", 123);
d.Add("S", 456);
foreach (var v in d)
{
    Console.WriteLine(v);
}

prints

[S, 456]
[s, 123]

rather than

[S, 456]

I personally don't have a strong opinion on this, the API just returns a snapshot. However, if we decide to change it, we could eliminate some extra copying when creating env var dictionary for process:

runtime/src/libraries/System.Diagnostics.Process/src/System/Diagnostics/ProcessStartInfo.cs

Lines 99 to 101 in e771b59

	_environmentVariables = new DictionaryWrapper(new Dictionary<string, string?>(
	envVars.Count,
	OperatingSystem.IsWindows() ? StringComparer.OrdinalIgnoreCase : StringComparer.Ordinal));

cc @GrabYourPitchforks

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I'm a bot. Here is a possible duplicate issue (I may be wrong):

• System.Environment.GetEnvironmentVariables() case sensitive but ProcessStartInfo.Environment/EnvironmentVariables insensitive #19142