Capture stackalloc size expression only if needed

LOC CHECKIN | roslyn - master | 20180112

Merge dev15.7.x to master

Move compiler core tests to use netstandard2.0 RTM

It was still relying on the 'ref' directory. Changed it to use the
resource image.

Merge dev15.7.x to master

Merge dev15.6.x to dev15.7.x

Now that the netstandard2.0 references are available via the
MS.CA.Test.Reosurces.Proprietary NuGet package we no longer need to copy
them around on the file system (that's where they were previously being
referenced from).

This changes the reference assemblies we use for the CoreClr compiler
compilation to be Net Standard 2.0 RTM. Previously they were a beta
version.

This did mean a number of tests had to be moved to be desktop specific
again. This is primarily due to the presence of ValueTuple as a default
type in Net Standard 2.0. Tests that relied on ValueTuple not being
defined had to be moved to net461 which doesn't have that type defined
by default.

Merge dev15.7.x to master

Constrain availability of ref conditional expressions to language versions 7.2 and higher

Merge dev15.6.x to dev15.7.x

Merge dev15.7.x to master

Fixes:#24306

Update string text for keybindings reset.

* make sure OOP inherit same culture as VS otherwise culture sensitive resource such as xml doc comment will not work properly

* don't crash on expected issue

Merge dev15.6.x to dev15.7.x

Fix a case where the stack spiller spills more than needed. (possibly resulting in false errors)

Add 15.7-vs-deps to published branches list

* dotnet/dev15.6.x:
  Fix symbol completion after 'in' (#24335)
  use PascalCase for const name
  Limit compiler server pipe name length (#24265)
  Test ConvertedType on LHS of deconstruction-assignment (#24158)
  remove unused usings
  use .editorconfig files
  address more comments
  address code review comments
  move newly added text into resource file
  add text and hyperlink to C# code style page

Merge dev15.6.x to dev15.7.x

Add a link to Tools>Options>…>Code Style to link to EditorConfig documentation. Bug#23513

On MacOS pipes are implemented using Unix domain sockets. Unix domain
sockets must have a valid file path for their endpoint. The best place
is in the temp folder. Unfortunately, domain sockets on Unix also have a
very small path length limit of 104 characters. In addition, Mac temp
paths can be very long since they include randomly generated characters
from the OS. In total, this means that Roslyn has barely 50 characters
worth of space for its pipe identifiers.

This change cuts down on the bytes of the SHA256 hash used. This shouldn't
affect the security of the pipe, since the hash isn't used as a security boundary,
but should fit the pipe name into the length limitations.

Fixes #24137