Fixes #14785

Fixes #14825

Merge dev15-rc into master

Fixing up our targets / settings file

Also clean up some grammar in Syntax.xml
Fixes #14651

Fix root path being truncated when formatting errors

Begin removing VSL name from build system

Disable Use Object Initializer diagnostic prior to C# 3

Fix casing of resource string.

fail fast when extension manager is null

fix error list navigation

made us to crash right away when extension manager is null to get better info on the situation.

if extension manager is null, vs is seriously broken.

fix https://devdiv.visualstudio.com/DevDiv/_workitems?path=Assigned%20to%20me&_a=query

in preview 5, error list navigation behavior has changed. this tweak roslyn side to accommodate the behavior change.

bug - https://devdiv.visualstudio.com/DevDiv/_workitems?id=284073&_a=edit

Merge dev15-rc into master

Then I better merge quickly.  ;-)

If it makes it in, great, if not then I guess we'll just get it in RC.2.

Report better telemetry for fix-all code actions.

Fixes: #13911

Non recursive tree serialization

Strip off underscores when generating constructors from fields.

Fixes #14219

SuggestedAction/CodeAction cleanup