Fix solution-based graph builds when non 'well-known' project types are used

[dfederm]

Fixes #9375

Previously, only projects which were SolutionProjectType.KnownToBeMSBuildFormat (handful of project type guids) would be considered. This would cause some projects in a sln to not be in the graph at all.

This change removes that check and in general brings solution-based graph construction slightly more aligned with how non-graph builds construct the metaproj (SolutionProjectGenerator). My ideal scenario would be that the graph would just directly call into SolutionProjectGenerator to create a metaproj and then use that as the entry point into the graph construction, but we would need to teach the metaproj the p2p protocol used for graph which is a bit more work. Maybe one day though :)

Change details:

• Removed the check for SolutionProjectType.KnownToBeMSBuildFormat
• Replaced the check for non-zero ProjectConfigurations with a call to SolutionFile.IsBuildableProject, which does that and also filters out SolutionProjectType.SolutionFolder
• Replaced the check for projectConfiguration.IncludeInBuild and SolutionFile.ProjectShouldBuild with a call to SolutionProjectGenerator.WouldProjectBuild, which does both those checks.

[rainersigwald]

My ideal scenario would be that the graph would just directly call into SolutionProjectGenerator to create a metaproj and then use that as the entry point into the graph construction, but we would need to teach the metaproj the p2p protocol used for graph which is a bit more work.

Agreed on both the ideal behavior and the decision to not do it right now.