This changes our pipelines to use the BYOC (Bring Your Own Cloud) pools
hosed by the core engineering team. This is a dynamic queue which should
scale better for our uses than the static pools we are using today.

Enable roll forward in our .NET Core exes

Restore fluent call depth

This changes our build to mark all of our .NET Core applications as
rolling forward on major / minor versions of the .NET framework.
Presently our tools ship inside both .NET Core 2 and 3 SDKs. This
setting allows our tools to run unmodified in both settings.

closes #25606

The change to move nullable to a two state solution inadverntently
changed how the CLR inlines a number of method calls. The combination of
not-inlining and over-inlining caused us to have a much larger "frame"
for analyzing a fluent call and exceeded our tolerance levels.

This adjusts the inlining so that we get the same results as before.

closes #33775

Classify paramref and typeparamref in Quick Info

* Address minor issues identified in review #32431.
Fixes #32807

Make ITestOutputHelper available to tests

Merge dev16.0 to master

fixed doesn't list 'assembly' keyword

Fixes #33546

Condense quick info

Close the Find Source window in case it's open

* Fixes #33601

* Respond to feedback

* Restrict to only trigger if identifier is in selection

* Respond to feedback

* respond to feedback

* Respond to feeback

Fix incorrect assertion in ContainedLanguage

See also #28798, #32047, #33879
Closes #29953

Simplify error message to not mention unconstrained type parameter that it doesn't apply to. (#33882)

Fixes #33847

Disable VirtualMemoryNotificationListener for Server GC

Merge dev16.0 to master

Split CloseFile into CloseCodeFile and CloseDesignerFile

Verifies that the current implementation matches the latest
LDM decisions on nullable suppression and out variables

Closes #27522

Use default literal for parameters in symbol display

Fixes #26442
Fixes #26443
Fixes #26444

Add an inline-description portion to regex-completion to make it easier to scan for the right choice

* Update PowerShell version

* Exit build.ps1 if PowerShell version less than 5

* Move check, tidy up formatting

This has shown up as a hot allocation path in a few different traces.
This change amortizes the allocations by using a pooled ArrayBuilder
instead of allocating a new Stack every time.

The following benchmarks seem to support the hypothesis:

Before change:

```
BenchmarkDotNet=v0.11.1, OS=Windows 10.0.17134.590 (1803/April2018Update/Redstone4)
AMD Ryzen 7 1800X Eight-Core Processor (Max: 3.60GHz), 1 CPU, 16 logical and 8 physical cores
.NET Core SDK=2.2.103
  [Host] : .NET Core 2.1.8 (CoreCLR 4.6.27317.03, CoreFX 4.6.27317.03), 64bit RyuJIT
  Core   : .NET Core 2.1.8 (CoreCLR 4.6.27317.03, CoreFX 4.6.27317.03), 64bit RyuJIT

Job=Core  Runtime=Core  Server=True

                Method |      Mean |     Error |    StdDev |     Gen 0 | Allocated |
---------------------- |----------:|----------:|----------:|----------:|----------:|
               Parsing |  65.25 ms |  1.301 ms |  2.568 ms |         - |   6.57 MB |
 CompileMethodsAndEmit | 634.00 ms | 12.640 ms | 22.468 ms | 1000.0000 |  40.29 MB |
     SerializeMetadata | 200.52 ms |  3.656 ms |  3.241 ms | 1000.0000 |  17.39 MB |
```

After change:

```
BenchmarkDotNet=v0.11.1, OS=Windows 10.0.17134.590 (1803/April2018Update/Redstone4)
AMD Ryzen 7 1800X Eight-Core Processor (Max: 3.60GHz), 1 CPU, 16 logical and 8 physical cores
.NET Core SDK=2.2.103
  [Host] : .NET Core 2.1.8 (CoreCLR 4.6.27317.03, CoreFX 4.6.27317.03), 64bit RyuJIT
  Core   : .NET Core 2.1.8 (CoreCLR 4.6.27317.03, CoreFX 4.6.27317.03), 64bit RyuJIT

Job=Core  Runtime=Core  Server=True

                Method |      Mean |     Error |    StdDev |     Gen 0 | Allocated |
---------------------- |----------:|----------:|----------:|----------:|----------:|
               Parsing |  67.26 ms |  1.344 ms |  3.321 ms |         - |   2.59 MB |
 CompileMethodsAndEmit | 627.23 ms | 13.307 ms | 23.995 ms | 1000.0000 |  28.85 MB |
     SerializeMetadata | 206.02 ms |  4.087 ms |  5.991 ms | 1000.0000 |  17.39 MB |
```

Introduce more efficient internal representation of a sequence VirtualChars

Remove unnecessary (duplicate) WaitForAsyncOperations