Fix building slnf with @ in the path

[surayya-MS]

Context

Fixes #11050

If the path to the solution file contains @, it builds normally. But, if solution filter references this solution then the build fails:

{my-path-to}/bugtest%40commithash/Solution/Solution.sln : Solution file error MSB5026: The solution filter file at "{my-path-to}/bugtest@commithash/Solution/Test.slnf" specifies there will be a solution file at "{my-path-to}/bugtest%40commithash/Solution/Solution.sln", but that file does not exist.

same happens with other symbols like % and $.

See the issue description for more details.

Details

The problem occurs on this line:

msbuild/src/Build/Construction/Solution/SolutionFile.cs

Line 661 in a1c2e74

return FileUtilities.GetFullPath(solution.GetProperty("path").GetString(), Path.GetDirectoryName(solutionFilterFile));

FileUtilities.GetFullPath changes @ to %40.

Specifically this happens here:

msbuild/src/Shared/FileUtilities.cs

Line 762 in 18c6b2e

string fullPath = EscapingUtilities.Escape(NormalizePath(Path.Combine(currentDirectory, fileSpec)));

Changes

Added bool escape param to FileUtilities.GetFullPath to be able to skip escape for getting solution path from solution filter (.slnf) json

Testing

Added new test to cover this scenario

[rainersigwald]

Could this be

Suggested change

	return FileUtilities.GetFullPath(solution.GetProperty("path").GetString(), Path.GetDirectoryName(solutionFilterFile), escape: false);
	return FileUtilities.NormalizePath(Path.GetDirectoryName(solutionFilterFile), solution.GetProperty("path").GetString());

without changing GetFullPath?

[surayya-MS]

this won't work because in GetFullPath before normalization the solution path that is provided in slnf needs to be fixed for the current machine.

msbuild/src/Shared/FileUtilities.cs

Line 759 in 04b6e1b

fileSpec = FixFilePath(EscapingUtilities.UnescapeAll(fileSpec));

I can create new function GetFullPathUnescaped and duplicate the code there. What do you think?