This is a breaking API change.  Need to decide if we want to take it or
not.

Turns out we could end up with the same IVisualStudioHostDocument
for both, if they are both added.

Fixes #19968.

When lowering local functions that capture struct frames, the frames are
added as ref parameters to the lowered method. Normally, when the local
function captures variables from multiple levels up the intermediate
closures are also rewritten to take the ref parameters. However, if one
of the intermediate closures captures no variables, the closure
conversion code can skip adding ref environments to that closure. This
can cause the inner-most closure to no longer have access to all of the
ref structs it expects, which crashes the compiler.

Fixes #18814, #18918

Merging master into dev15.3.x for final stabilization

Add entries for dev15.3.x branch in readme.md

Don't assume a document has SyntaxFactsService

Skip CSharpInteractive.TypingHelpDirectiveWorks test

Improve performance of inline rename with multi-targeting

If it doesn't, just use case sensitive matching

Update list of branches for myget publishing

Don't fetch every PR ref for every PR job

Newer versions of git (I've seen this behavior on 2.13.1.windows.1 and
have not seen it on 2.11.1.windows.1) are much slower at writing out local
copies of refs after a fetch. Given that we fetch about 10K refs when
running each PR job this can lead to a massive slowdown in fetch times (on
the roslyn integration job, which has a newer version of git on the
workers compared to the other machines, we see fetch taking ~20 mins).

This changes all the Roslyn jobs to fetch just the PR they are going to
test, which speeds up the fetch significantly.

Clear completion pattern matcher caches on solution close

get ParseOptions from ProjectState rather than calculate one itself

Skip deriving IArgument if there's error in parameter type

Cast the correct object to IVsBrowseObjectContext

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.

Fix a typo in the Build NuGet script

Add build status for the dev15.6 branch

Don't crash and send an NFW if debugger contenttype does not match

Updating VSIXExpInstaller to 0.4.0-beta

Updating BuildAndTest.proj to explicitly uninstall extensions from a previous build before installing new ones.

Capture exception info for integration test failures

Will capture the exception stack trace in addition to the screen shot
when a first chance exception occurs running our integration tests.

Support adding PackageReferences to CPS projects

Add support for inspecting Solution Explorer items

We need this version to avoid conflicts with other assemblies that
reference a different version of the System.Composition.* assemblies.

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