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.

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

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

* handling empty accessors and bodies

* removing unused internal parameter

Add test documentation to the PR template

Fix crash in VisualBasic.Binder.MemberLookup.AddLookupSymbolsInfoInTypeParameter when it is called with Cref TypeParameter. (#21586)

Fixes https://devdiv.visualstudio.com/DefaultCollection/DevDiv/_workitems?id=410932.

The fix mimics the way C# compiler handles Cref TypeParameters in the similar API.

3 product changes and 1 test change on sqlite persisted storage

removed usage of ImmutableArray in json.net

Update to Microsoft.DiaSymReader.PortablePdb, Microsoft.DiaSymReader.Converter.Xml to 1.4.0-beta1-62016-01 (#21557)

Perform synthesis of closure methods in an early pass before visitation,
meaning we no longer need to do a second visitation of the tree to lower
local functions.

The baselines have been changed because we now do closure id and
synthessis in order of closure visitation, rather than bound node
visitation. Closure visitation visits all the closures in a given scope,
then recurs into nested scopes, while BoundNode visitation treats
closures as scopes themselves, so nested closures are visited before
closures declared in the same scope.

Fixes https://github.com/dotnet/roslyn/projects/26#card-3753331

Merge dev15.4.x to master

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.