Don't offer to inline _ as that could become a discard.

Pass along appropriate loc strings for the 'use pattern matching' code actions.

Better codify brace matching invariants.

Support getting and setting Module accessibility through the SyntaxGenerator

Change s_FieldModifiers filter to accept WithEvents modifier on VB fields
Fixes https://github.com/dotnet/roslyn/issues/18159

Use dotnet-bot instead of vslsnap GitHub account for GithubMergeTool

Do not capture pinned locals into state machine

Removes our reliance on the machine installed reference assemblies.
Preferring the ones which we bring with us to the machine for both
Windows and Linux.

Now that MSBuild has a way of flagging warnings as errors we will use
this over our custom check-msbuild script.

Powershell has two methods of detecting error that have very different
semantics:

- $?: bool which represents status of last powershell operation
- $lastexitcode: integer holding exit value of last windows command

When Powershell directly executes a windows command these two variables
are roughly interchangable.  For example:

``` cmd
> & msbuild BadProj
> "$?:$lastexitcode"
false:1
```

When Powershell indirectly executes a windows command, say through
Invoke-Expression, then the important differences show up.  The $?
variable will represent Invoke-Expression while $lastexitcode will
represent the windows command.

``` cmd
> Invoke-Expression "& msbuild BadProj"
> "$?:$lastexitcode"
true:1
```

Updated the error checking around Exec to guard against this potentiall
difference.

Adding tests that demonstrate behavior of stackalloc in using-statements