Fixes #26442
Fixes #26443
Fixes #26444

See #33785

See #30599

See #33597

(cherry picked from commit de8e5531)

This change improves integration test reliability by ensuring the
debugger is terminated prior to attempting to close a solution.

This change replaces the use of DTE with VsShellUtilities.OpenDocument
for opening a file in design mode.

Integration tests now ignore error list entries not associated with a
project, since these entries should have been cleared when the solution
closed.

This workaround should be removed when #32121 is resolved.

Closes #18996
Closes #19090
Closes #19091

# Conflicts:
#	src/NuGet/Bootstrap.csproj
#	src/NuGet/BuildNuGets.csx

This change updates the file open implementation use VsShellUtilities.OpenDocument.
DTE plus waiting for the active window title alone proved insufficient, where some
tests were incorrectly operating on the previous active document.

Fixes #19191
Fixes #26037

This change updates the code to use ProjectItem.Open instead of relying on
the asynchronous File Open command. Prior to the change, the method would
occasionally return early, allowing the caller to modify the previous active
document before the newly opened document was fully activated.

Fixes #26037

We're trying to go from an `IVsBrowseObjectContext` to an `IPackageReferencesService`.
We were doing this through `IVsBrowseObjectContext.ConfiguredProject`, but it turns out
that this property always returns null on the particular implementation of
`IVsBrowseObjectContext` we're working with.

Instead, we need to go through the `UnconfiguredProject` and ask it for the "suggested"
`ConfiguredProject`.

I've also switched from `GetAwaiter().GetResult()` to properly async/await code inside
an `ExecuteSynchronously` call, mostly for the purposes of readability.

According to [Finding CPS in a VS project](https://github.com/Microsoft/VSProjectSystem/blob/master/doc/automation/finding_CPS_in_a_VS_project.md)
we should cast an `EnvDTE.Project` instance directly to `IVsBrowseObjectContext`. Currently we take the
object returned by `EnvDTE.Project.Object` and cast that, but this seems to only be valid for VC projects.

We're on a background thread already, so we can just block on the calls to `AddAsync` and `RemoveAsync`.

Add APIs to allow integration tests to add PackageReferences to CPS projects.

Add basic support for inspecting Solution Explorer items.

The operation in CPS is asynchronous, so we need to wait like we do in
other places.

We were being imprecise where operations on a file path were finding
the first one with that file name, even if it was from the wrong
project.

Integration tests: BoxSelection, CSharpInteractiveDirectives, CSharpInteractiveFormsAndWpf, CSharpReplClassification, CSharpInteractiveCommands, REPL Intellisence, CSharpSendToInteractive  (#18137)

CSharpInteractiveCommands, REPL Classification and REPL Intellisence integration tests

Also adds an "AddProjectReference" helper to the SolutionExplorer
classes, and an "UndoLastGlobalAction" helper to the Editor classes.