Fixes condition that checks whether PDB and sources are out of sync.
Converts the line character position (which is relative to line start)
to a position relative to file start in order to compare it with
sourceLines.

Methodology: sync to  4cb203da , add any lines appearing in
PublicAPI.Unshipped.txt to master's PublicAPI.Shipped.txt and remove them
from master's PublicAPI.Unshipped.txt, re-sort.

This change does the following:

- Deletes the constructor WorkItem(int) leaving only WorkItem(int, string).
- Fixes up many occurences where the URL of the bug was missing / incorrect.
- Removes several WorkItem attributes that had invalid bug ids

ResetInteractive base class is not coupled to VS and therefore is much easier to test.

now we will show <Unknown> for such project.

fixed a crash where diagnostic source is removed but asked new snapshot from error list in two different snapshot

Manually inspected the WorkItem values and added the appropriate URL.

now, we will automatically re-enable full solution analysis (if user didn't explicitly disabled it) when new solution is opened.

by removing `<DebugType>` lines from projects that import `VSL.Settings.targets`

user can either explicitly turn it back on or re-start VS to re-enable the full solution analysis.

THese helpers were used to make VB workspace construction easier when VB didn't have
an easy way to make multi-line strings.

Now htat VB can make multi-line strings, we no longer need these entrypoints.

The Roslyn build machines are still currently using VS2015 RTM, which
does not have IExpansionManager.

Fixes #6685

Calling IVsTextManager2.GetExpansionManager can return either an IVsExpansionManager or an IExpansionManager, and we now support reading snippet info from both.

In the IVsExpansionManager case, we behave as before this change. During package load, we kick off a task to execute later on the UI thread to synchronously enumerate the snippets.

In the IExpansionManager case, we instead enumerate the snippets asynchronously on a background thread.

For Visual Studio 2015 Update 1 RTM, we will only receive an IVsExpansionManager. Starting with Update 2 (and with some intermediate builds) we will receive IExpansionManagers by default, but the platform reserves the right to return an IVsExpansionManager as a fallback, so we must continue to support both. Because IExpansionManager already existed in Update 1, we do not need to do adaptive light-up to keep this code working on Update 1.

Adds a disposable wrapper around ITextView to avoid writing try ...
finally... everywhere.

the race itself already existed but this PR made the race to surface.

This is quick fix to prevent throwing asserts if CPS has changed the
foreground SynchronizationContext.