This reverts commit 64b95c62.

Use DOTNET_HOST_PATH as the full path to dotnet, not the containing dir

Do not offer ?. if it changes a value to a nullable.

Initial clean up of workspaces desktop

Optimize performance for LookupSymbols(name) 

A customer trace on recent 15.3 release shows that `Microsoft.CodeAnalysis.CSharp!Binder.IsAccessibleHelper` is taking up large amount of CPU stacks for LookupSymbols(name) calls from IDE analyzers. This change optimizes the performance of this code path by adding a name check before doing accessibilty checks.

Remove obsolete MEF v1 method of exporting options: [ExportedOption]

Optimize performance for LookupSymbols(name)

Typo

Do not offer 'use throw expression' if value is accessed before being checked for null.

Give link to new Manual Testing document

Delete some unused references in EditorFeatures

Don't offer 'generate overrides' in a static class.

Don't offer to use pattern matching if a user defined operator was involved.

merge dev15.3.x to dev15.4.x

Fix no completion in partially written code before 'await'.

removed ImmutableArray from json.net usage. and moved to IList

* parameter refness update in local funcitons/lambda should be caught as an edit

* handling empty accessors and bodies

* removing unused internal parameter

Merge dev15.3.x to dev15.4.x