Merge dev15.9.x to master

Update ICSharpCode.Decompiler to 4.0-beta1

Add a code refactoring to convert local function to method

Closes #29030

Correct the XML tags for the list of exceptions

trim extra lines between copyright and namespace (#23568)

Merge dev15.8.x to dev15.9.x

Add the Roslyn naming conventions to .editorconfig

Fixes dotnet/docs#6228

The text inside of the `<item>` is removed from the docs site because the `<item>` tag does not contain a child `<description>` element.

Fix signing info

Fixed remaining case for 'Use local function' refactoring.

Move portable facade validation

Introduce-var should work when caret is on the right of an expression.

This ensures the F# package is loaded for CPS only projects in a solution. Seems this was an oversight.

Independent of Microsoft/visualfsharp#5391, ensuring the F# package load fixes this issue: Microsoft/visualfsharp#5395 - and it probably fixes other issues that we haven't discovered as a result of not loading the package.

Merge dev15.9.x to master

Add check for symbol.IsOverride when renaming a symbol

Merge dev15.8.x to dev15.9.x

Delete Contract.* methods that are equivalent to Debug.Assert

Expose way to add custom JsonConverters to support external Roslyn OOP services

These can be very confusing, since other methods on Contract actually
throw exceptions. Since we have endless amounts of code directly calling
Debug.Assert, let's just use it everywhere.

Prioritize NavigateTo searches to care most about the current actives docs/project.

README update

Update Build.proj

Merge dev15.8-preview4 to dev15.8.x

* Precedence: explicit selection -> provider preference -> last selection -> first/default value.
* Remove logic to bail out on retrigger

Merge dev15.9.x to master