This change skips executing analyzers by default on explicit builds (both inside VS and on command line prompt). This should speed up the overall build time of Roslyn.sln when building locally.

The only time a developer would want analyzers to run locally outside the typing scenario is to compute the exact set of warnings for a specific project/solution before pushing your local changes to CI. They can now perform the following steps to achieve this:
1. On command line: Build with `/p:UseRoslynAnalyzers=true` or `/p:RunCodeAnalysis=true`
2. Inside VS:
   1. Start VS with `%RoslynEnforceCodeStyle% = true`, all builds in VS should execute analyzers
   2. Use `Run Code Analysis` command from `Analyze` menu on selected project/solution

Merge release/dev16.7-preview1 to master

Fix regression using alias qualified name in an is-type expression

Merge release/dev16.7-preview1 to master

Use a shared shadow copy assembly loader for all VisualStudioAnalyzer…

Fixes #44019

🧹 Remove duplicate calls to ThrowIfCancellationRequested

Fix declared dependencies of Microsoft.VisualStudio.LanguageServices

Fixes VSO [#1109876](https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1109876)
Verified manually that we no longer generate the CS8032 warnings for projects referencing analyzer assemblies with analyzer dependencies.

NOTE: This is a targeted fix for 16.7 Preview1. We can potentially add a regressiont test for this scenario to verify that all VisualStudioAnalyzer instances share the same shadow copy assembly loader. However, @tmat is planning to soon delete VisualStudioAnalyzer and avoid loading analyzers in devenv process, so this code will go away soon.

Fix MEF usage in more tests

Show hyperlinked diagnostic IDs in Quick Info

Merge release/dev16.7-preview1 to master

Add warning message if semantics may change due to inline temporary variable refactoring

Fix regression in global:: qualified constant in a switch case.

Only run code style analyzers when nullable warnings are enabled

Fix a native integer decoding bug

We were incorrectly emitting our dependency of
Microsoft.VisualStudio.Composition and Microsoft.CSharp; instead of
pointing to the version that we were actually consuming, we were
emitting our version in place of version we depending on.

* Allow msbuild to pass properties and metadata as analyerconfig:
- Add new target to evaluate requested properties and metadata
- Add new task to turn collected evaluations into a global analyzer config
- Add tests

Bump prerelease version for 16.7 preview 2

Remove trailing space from BoundDecisionDagNode

Introduce explicit downcast to VB .NET

Don't cache FileInfo instances.

Update Contributing-Code.md

Merge release/dev16.7-preview1 to master

Fix API issues identified during API review

Enforce analyzer consistency in our builds

Add 16.7 Preview 1 to the publish data config