Avoid stealing focus from the active output window pane

Rename KeyValuePair

The target framework netcoreapp2.0 includes a new type: `KeyValuePair`.
This conflicts with our `KeyValuePair` utility class and causes a lot of
friction whenever netcoreapp2.0 is added as a target framework for a
project.

Renaming the type to `KeyValuePairUtil` to remove the ambiguity.

Enable C# semantic tests on CoreClr

The syntax is incorrect and it's failing bash. Will try again later.

Make "Roslyn" default setup project

This isn't used by anything else.

Update CSharpFullyQualifyCodeFixProvider to support unbound identifier diagnostics

Simplify impl of 'prefer predefined type'

Check for invalid file paths in ContainsChildrenGraphQuery

Implement INavigateToItemProvider2 with filtering

Reduces the implicit double check for invalid characters in the path.

Fix target instance selection for integration tests run from test explorer

Enable VB symbols test on CoreClr

Fix a build warning related to an unused event that implements an interface event

Update 'use conditional expression' to work for 'yield' statements.

Use a synthesized local for the lockTaken parameter and create a region for it

Fix spanish build

Avoid producing a new tag tree for buffers that aren't part of the SpansToTag

By default, VS sets the first project listed in the solution as the default project. This saves new contributors from having to manually set the default project.

Fix issues with the windows_loc_status check

* `buffers` is an unnecessary intermediate variable. Any text buffer present in `buffersToTag`
  but not also present in `buffers` will end up ignored by `ComputeNewTagTree`, and thus not
  influence the result of `ConvertToTagTrees`. Based on this, `buffers` was eliminated to
  simplify the implementation.
* When `spansTagged` has only a single span, it's possible that other tag trees in `oldTagTrees`
  need to propagate forward. The early return failed to account for this, and if hit would drop
  `oldTagTrees` tags for buffers not equal to the buffer from `spansTagged`. In addition, the
  early return failed to account for the case where `spansTagged` only contained a single
  span from a buffer not requested per `buffersToTag`. Following the elimination of `buffers`,
  the value of a special case handling here was notably reduced and the edge case was simply
  eliminated in favor of the remaining code in the method.
* The patter of Select followed by ToLookup was replaced by a single call to ToLookup specifying
  both the keys and the values of the resulting lookup.

1. __UNITTESTEXPLORER_VSINSTALLPATH__
2. VSAPPIDDIR (new for this commit)
3. VSInstallDir