ProjectInSolution.AbsolutePath should return a normalized full path

[jeffkl]

Issue Description

ProjectInSolution.AbsolutePath currently returns the result of Path.Combine() which leaves in relative path segments like ..\. When parsing a solution and getting the paths to projects, this places the burden on the caller to normalize the path.

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

Line 165 in 1ff34e8

public string AbsolutePath => Path.Combine(ParentSolution.SolutionFileDirectory, RelativePath);

Steps to Reproduce

Create a solution with relative paths containing ..\
Parse the solution with the SolutionFile API
Call the AbsolutePath property on one of the ProjectInSolution objects.

Expected Behavior

AbsolutePath property returns a normalized full path.

Actual Behavior

AbsolutePath property returns a path containing ..\ segments.

Analysis

Versions & Configurations

All versions of MSBuild

This manifested into this bug: NuGet/Home#10307

And its worked around in MSBuild's own codebase:

msbuild/src/Build/Graph/GraphBuilder.cs

Lines 293 to 298 in 1ff34e8

	new ProjectGraphEntryPoint(
	FileUtilities.NormalizePath(project.AbsolutePath),
	solutionGlobalProperties
	.SetItem("Configuration", projectConfiguration.ConfigurationName)
	.SetItem("Platform", projectConfiguration.PlatformName)
	));

[aolszowka]

Wonder if these are related?

#5915

Also #5898