SelectMany diagnostic, `ref` overload, allowed member modifiers

Merge master into features/extensionEverything

Fix command line parsing of quoted values

Extension everything feature cleanup

Add extra logging to invocation of ibcmerge...

Add partial-type-name suggestions to C# and some fixes for VB

Merge dev15-preview-4 into master

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Fix a bad merge

removed stale references to Concord.csproj

This is causing signing to fail without any messages.  Not on the critical path.

Move Roslyn.VisualStudio.Setup.Interactive.dll to be regular signed

Ensure IBC is running for our official builds.

There will be a corresponding update to the Build Definitions to provide the $(IbcMergePath) value.

Merge dev15-preview-4 into master

Previously, a tuple in a declaration context always required a
TupleElementNamesAttribute to record the names. Now, when the tuple has
no names the compiler will elide the attribute. On loading from
metadata it is assumed that tuples without an attribute have no names.

Fixes #12454

Add binding redirect for System.Collections.Immutable

# Conflicts:
#	src/Tools/SignRoslyn/BinaryData.json

Merge microupdate into dev15-preview-4

Merge microupdate into master

Refactor completion commit.

Add support for switching on float, double, and decimal.

Refactor how we do completion set filtering.

# Conflicts:
#	src/Workspaces/Core/Portable/SymbolId/SymbolId.cs
#	src/Workspaces/CoreTest/SymbolKeyTests.cs

# Conflicts:
#	src/Workspaces/Core/Portable/SymbolId/SymbolId.cs

Temporarily disable IBC merge.