Merge dev15.6 to master

Fixed file sharing on F# projects, removes annoying message that file is open in another project (#4025)

* Fixed file sharing on F# projects, CPS and legacy.

* Added a comment on FSharpEditorFactory

* Fix collapsed range for constructor invokations

* Add collapsed ranges to tests

Made this readme a lot less cryptic and a lot more up to date.

Update DEVGUIDE.md

Merge master to dev15.6

Merge dev15.6 to master

* remove test dependency on peverify.exe

* enable metadata-only validation

Corrected wording on the component to install and cleaned up some whitespace.

Use ConcurrentDictionary in deduplicate names

reenable delay signing and `sn -Vr` for build assemblies to speed up local work

Merge master into dev15.6

* Merge branch 'combine-sparse-open-decls-and-hash-directives' into rider

# Conflicts:
#	src/fsharp/TypeChecker.fs

* add Structure tests

remove test dependency on sn.exe

only public sign assemblies, not test sign

normalize backslashes in .nuspec files

publish non .nupkg insertion items

This cleans up a bunch of build warnings saying that nothing could be found in the `lib\` directory.

Update feed tasks version

ensure the expected dotnet CLI is actually present

* fix FSharpMemberOrFunctionOrValue.IsConstructor property for ctor definition

* add a test

Contains various bug fixes

This reverts commit d8544fe2.

* add static members to the extended completion

* provide static method in completion for any type