* split out language service into dedicated dir

* dedicated extensions module

* trim pervasive

* rename constants

* symbols module

* typedastutils module

* FSharpChecker extensions

* rename roslyn helpers

* editor rename cleanup

* fix test renaming

* show proper glyphs for namespaces and structures

* glyphs for literals and delegates

* fix layout for struct records and unions

* proto does not like Option.defaultValue

* show [<Struct>] in layout instead of "struct" for struct records and DUs

* show proper glyph for operators in QuickInfo

* fix test compilation

* layout `Measure` and `Struct` special attributes as types

prettier records layout

* fix a test

* Revert records layout change

* fix TypeChecker

* do not print [<Struct>] for ordinary structures

* UnusedOpensDiagnosticAnalyzer

* it works

* remove unused code

refactor

* RemoveUnusedOpens Code Fix

* fix crash on EnclosingEntity

* refactoring

* add Seq.toImmutableArray combinator

* bug fix

handle nested modules

* fixed: it does not work on attributes

remove unused opens

* dog food

* filter out symbol uses which have the same range, but different occurrence kinds

* add a comment

* enable Roslyn's non blocking code complete

update Microsoft.CodeAnalysis.xxx packages to version 2.0.0-rc3-61225-01

* update references from `IFindReferencesService` to `IFindUsagesService`

* use asyncMaybe everywhere

* fix compilation

* continue the refactoring

* finish the refactoring

* fixed: AsyncMaybe.Delay was not lazy

* fix tests

fixed: Find All References does not search symbol usages in the project(s) the symbol is declared (#2139)

* port lexer symbol lookup logic from VFPT and use it in DocumentHighlightsService

* QuickInfoProvider uses lexer symbol

* remove tryClassifyAtPosition

* do not show quick info if FCS return a list of single FSharpTooltipElement.None

* use standard Option combinators

remove Pervasive.fs

fix FSharpSymbol.IsPrivateToFile