Merge dev15-rc2 into master

* Add instructions for getting an Insider VSIX

This is required to get a good IDE experience now that we're using C# 7 in the compiler.

* Update directions

* Specify the RC VSIX as the one to install

Do not offer UseObjectInitializer if it would change implicit-member-access semantics.

Fixes #15012

Move 'Add Braces' to the new FixAll' system.

Move 'UseImplicitType' onto the new FixAll system.

Pull common FixAll logic into some helper base types that we can use across many of our code style fixes.

Pull common FixAll logic into some helper base types that we can use across many of our code style fixes.

Address outstanding issues around custom modifiers in VB.

Start using Tuples in IDE code.

Run the 'use expression body' analyzer OOP.

MakeRValue should be applied to tuple literals recursively

Clear out our projection buffers when we shutdown the pr eview window to workaround an editor bug.

Merge dev15-rc2 into master

Localize strings in DataGrid headers