Merge release/dev17.12 to release/dev17.13 (#11258)

This is an automatically generated pull request from release/dev17.12
into release/dev17.13.


Once all conflicts are resolved and all the tests pass, you are free to
merge the pull request. 🐯

## Troubleshooting conflicts

### Identify authors of changes which introduced merge conflicts
Scroll to the bottom, then for each file containing conflicts copy its
path into the following searches:
- https://github.com/dotnet/razor/find/release/dev17.12
- https://github.com/dotnet/razor/find/release/dev17.13

Usually the most recent change to a file between the two branches is
considered to have introduced the conflicts, but sometimes it will be
necessary to look for the conflicting lines and check the blame in each
branch. Generally the author whose change introduced the conflicts
should pull down this PR, fix the conflicts locally, then push up a
commit resolving the conflicts.

### Resolve merge conflicts using your local repo
Sometimes merge conflicts may be present on GitHub but merging locally
will work without conflicts. This is due to differences between the
merge algorithm used in local git versus the one used by GitHub.
``` bash
git fetch --all
git checkout -t upstream/merges/release/dev17.12-to-release/dev17.13
git reset --hard upstream/release/dev17.13
git merge upstream/release/dev17.12
# Fix merge conflicts
git commit
git push upstream merges/release/dev17.12-to-release/dev17.13 --force
```

src/Razor/src/Microsoft.VisualStudio.LanguageServices.Razor/ProjectCapabilityResolver.cs

@@ -111,6 +111,15 @@ internal sealed class ProjectCapabilityResolver : IProjectCapabilityResolver, ID
             return false;
         }
 
+        // vsHierarchy can be null here if the document is not included in a project.
+        // In this scenario, the IVsUIShellOpenDocument.IsDocumentInAProject(..., ..., ..., ..., out int pDocInProj) call succeeds,
+        // but pDocInProj == __VSDOCINPROJECT.DOCINPROJ_DocNotInProject.
+        if (vsHierarchy is null)
+        {
+            _logger.LogWarning($"LSP Editor is not supported for file because it is not in a project: {documentFilePath}");
+            return false;
+        }
+
         try
         {
             return vsHierarchy.IsCapabilityMatch(capability);