Option to avoid "fixing" \ in new TaskItem()

[rainersigwald]

Summary

This code unconditionally calls FixFilePath:

msbuild/src/Utilities/TaskItem.cs

Lines 80 to 86 in 4c6a5a9

	public TaskItem(
	string itemSpec)
	{
	ErrorUtilities.VerifyThrowArgumentNull(itemSpec);
	_itemSpec = FileUtilities.FixFilePath(itemSpec);
	}

But while TaskItems usually represent files on disk, they don't necessarily do so, and if they don't and also contain backslashes this will corrupt them. It should be configurable.

Background and Motivation

See analysis by @JoeRobich in dotnet/roslyn#72014 (comment).

Proposed Feature

        public TaskItem(
            string itemSpec
+           bool convertBackslashesToSlashes = true)
        {
            ErrorUtilities.VerifyThrowArgumentNull(itemSpec);

+           if (convertBackslashesToSlashes)
+           {
                _itemSpec = FileUtilities.FixFilePath(itemSpec);
+           }
        }

Alternative Designs

No response

[jeffkl]

I suggest the name of the input parameter to be bool treatAsFilePath = true and document as such that MSBuild will by default treat it as a file path and potentially "fix" it up and/or create a full path from it.