They can call the public entry point instead.

If we failed to get a document moniker for the contained document, fail
now.  Otherwise we'd crash when attempting to create a document key.

Switching to IVsProject.GetMkDocument to get document moniker instead of
iterating through all the entries in the running object table. Also
cleaning up a bit of code while I'm here - It looks like we don't need
to determine Shared Hierarchy & Shared ItemId here anymore. It was there
for error list and it looks like with PR #2399 error list switched to a
different implementation.

If IVsHierarchy.ParseCanonicalName returns something other than S_OK,
then use VSITEMID.Nil

we will move away from IVsHierarchy and start to use ProjectIdGuid instead.

Refactoring the code a bit. Pushed the mapping of hierarchy to shared hierarchy and itemId to shareditemId into LinkedFile Utility class. So now we give a hierarchy, itemId pair and get back a sharedhierarchy, itemId pair.

For a shared item that is a contained document, use the correct itemId and hierarchy to get a document moniker from running document table.

previously we reported actual project (active context project in case of project k/shared project) to error list. this should let error list to only show errors for one specific project when current project filtering is set.

but right now error list uses IVsHierarchy of project k/shared project rather than active context. so for RC, we will do that. that means for project k/shared project, we will show errors for all context (multiple projects)  when the filtering is set.

for RTM, we will resolve design issue of what "Current Project" filtering means for error list.

Of course, a ContainedLanguage will never be an IProjectionBuffer. So,
this method always returns an empty enumerable. Instead, the cast should
be against _containedLanguage.DataBuffer.

#hangsheadinshame

Workflow XOML files call into IVsContainedLanguageFactory.GetLanguage(),
passing an IVsTextBufferCoordinator. However, that
IVsTextBufferCoordinator is constructed differently than the one we get
from Venus and breaks some assumptions in the C#/VB language services.

The critical assumption that XOML breaks is that the primary buffer is
an IProjectionBuffer. This is not true for XOML. Instead, it is simply a
non-projected buffer with the HTML content type.  So, our code attempts
to cast to an IProjectionBuffer and we crash before ever creating a
ContainedDocument and adding it to the workspace. To fix this, we need
to break the IProjectionBuffer assumption and update any calling code
depending on projections to dynamically cast to IProjectionBuffer first.
This unblocks several Workflow v1 scenarios.

Next, it turns out that XOML never calls SetHost() on the
IVsContainedLanguage that we return. So, there's never an
IVsContainedLanguageHost hooked up and calling code needs to be updated
to guard against null hosts.

Fix #409:
Add explicit StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase where it was intended,
or replace single-char string literals with chars literals.
Also, provide InvariantCulture in TryParse where it was intended.