Share file header analyzer with the code style layer

Add a comment to the newly added asserts related to editorconfig options

Port RemoveUnnecessaryImports analyzer/fixer/tests to shared layer

Use proper asynchronous methods in PreviewFactoryService

Port C# UseImplicitType and UseExplicitType analyzers to shared layer

Limit cascading when finding the set of members to update when switching member to be explicit.

* Update dependencies from https://github.com/dotnet/arcade build 20200304.1

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20154.1

* Update dependencies from https://github.com/dotnet/arcade build 20200305.4

- Microsoft.DotNet.Arcade.Sdk - 5.0.0-beta.20155.4
Co-authored-by: Ndotnet-maestro[bot] <dotnet-maestro[bot]@users.noreply.github.com>

Add finer-grained cancellation token checks during some find operations

Implement file header analyzer

Fix official build

Port RemoveUnnecessaryCast analyzer/fixer/tests to shared layer

Support conditionally invoked indexers in Find-All-References.

Disable Navigate-To filtering of previous results.

Delete LinkedFileDiscrepancyException

Add support for "remove unnecessary cast" simplifying 'as' expressions.