Update vendored System.Memory (#8459)

## Summary of changes

- Update the System.Memory based on NuGet package sources

## Reason for change

We want to update our vendored .NET library versions.

## Implementation details

- Make the vendoring repeatable
- Run the tool, check for errors, tweak, rinse and repeat
- After running the tool, used 🤖 to identify segments of code that
weren't used, so we could strip them out

The updated vendoring is based on the public
[System.Memory](https://www.nuget.org/packages/System.Memory/4.6.3#dependencies-body-tab)
nuget package, so is designed to be used with .NET Framework and .NET
Standard, so makes the most sense to use IMO.

As this package also uses _System.Buffers_ and
_System.Numerics.Vectors_, vendored those pieces we need where
appropriate.

## Test coverage

This is the test, if it compiles and tests pass, we should be ok 🤞

## Other details

https://datadoghq.atlassian.net/browse/APMLP-1207

Note that currently, there's a lot of `Utf8Formatter` code that _isn't_
used, and could be excluded, however, given that theoretically we
could/should use this in the future. I'm torn whether to just leave it
in, or whether to tear it out for now, and restore it if/when we want to
use it later. Any thoughts?

Part of a stack updating our vendored system code

- #8391
- #8454
- #8455

Author: andrewlock

tracer/build/_build/UpdateVendors/VendoredDependency.cs

@@ -34,8 +34,14 @@
     <!-- https://www.nuget.org/packages/System.Collections.Immutable/7.0.20 -->
     <PackageReference Include="System.Collections.Immutable" Version="7.0.20" />
 
-    <!-- https://www.nuget.org/packages/System.Memory/4.5.5 -->
-    <PackageReference Include="System.Memory" Version="4.5.5" />
+    <!-- https://www.nuget.org/packages/System.Buffers/4.6.1 -->
+    <PackageReference Include="System.Buffers" Version="4.6.1" />
+
+    <!-- https://www.nuget.org/packages/System.Numerics.Vectors/4.6.1 -->
+    <PackageReference Include="System.Numerics.Vectors" Version="4.6.1" />
+
+    <!-- https://www.nuget.org/packages/System.Memory/4.6.3 -->
+    <PackageReference Include="System.Memory" Version="4.6.3" />
 
     <!-- https://www.nuget.org/packages/System.Private.CoreLib/1.0.0 -->
     <PackageReference Include="System.Private.CoreLib" Version="1.0.0" />

tracer/dependabot/Datadog.Dependabot.Vendors.csproj

@@ -101,7 +101,7 @@
 
   <!-- we don't need the vendored .NET runtime code when targetting .NET Core 3.1+ -->
   <PropertyGroup>
-    <DotNetRuntimeFiles>Vendors/System.Collections.Immutable/**;Vendors/System.Memory/**;Vendors/System.Private.CoreLib/**;Vendors/System.Reflection.Metadata/**;Vendors/System.Reflection.Metadata.Interop/**;Vendors/System.Runtime.CompilerServices.Unsafe/**</DotNetRuntimeFiles>
+    <DotNetRuntimeFiles>Vendors/System.Buffers/**;Vendors/System.Collections.Immutable/**;Vendors/System.Memory/**;Vendors/System.Numerics.Vectors/**;Vendors/System.Private.CoreLib/**;Vendors/System.Reflection.Metadata/**;Vendors/System.Reflection.Metadata.Interop/**;Vendors/System.Runtime.CompilerServices.Unsafe/**</DotNetRuntimeFiles>
   </PropertyGroup>
 
     <ItemGroup Condition="$([MSBuild]::IsTargetFrameworkCompatible($(TargetFramework), 'netcoreapp3.1'))">

tracer/src/Datadog.Trace/Datadog.Trace.csproj

@@ -77,4 +77,12 @@ public CompilerFeatureRequiredAttribute(string featureName)
 
     public bool IsOptional { get; init; }
 }
+
+// Calls to methods or references to fields marked with this attribute may be replaced at
+// some call sites with jit intrinsic expansions.
+// Types marked with this attribute may be specially treated by the runtime/compiler.
+[AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Field, Inherited = false)]
+internal sealed class IntrinsicAttribute : Attribute
+{
+}
 #endif

tracer/src/Datadog.Trace/Util/System.Runtime.CompilerServices.Attributes.cs

@@ -0,0 +1,21 @@
+## About
+
+Provides resource pooling of any type for performance-critical applications that allocate and deallocate objects frequently.
+
+## Main Types
+
+The main types provided by this library are:
+
+- System.Buffers.ArrayPool<T>
+
+## Additional Documentation
+
+- API reference can be found in: https://learn.microsoft.com/en-us/dotnet/api/system.buffers
+
+## Related Packages
+
+ArrayPool is shipped as part of the shared framework starting with .NET Core 3.1.
+
+## License
+
+System.Buffers is released as open source under the [MIT license](https://licenses.nuget.org/MIT).

tracer/src/Datadog.Trace/Vendors/System.Buffers/PACKAGE.md

@@ -0,0 +1,21 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum);netstandard2.1;netcoreapp2.0</TargetFrameworks>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <StrongNameKeyId>Open</StrongNameKeyId>
+    <AssemblyVersion>4.0.2.0</AssemblyVersion> <!-- NO-INCREMENT: This version is frozen for netstandard2.0. -->
+    <IsPlaceholderTargetFramework Condition="'$(TargetFramework)' == 'netstandard2.1' or '$(TargetFramework)' == 'netcoreapp2.0'">true</IsPlaceholderTargetFramework>
+  </PropertyGroup>
+
+  <!-- Package servicing properties -->
+  <PropertyGroup>
+    <IsPackable>false</IsPackable>
+    <VersionPrefix>4.6.1</VersionPrefix>
+    <VersionPrefix Condition="'$(IsPackable)' == 'true'">4.6.2</VersionPrefix>
+    <AssemblyVersion Condition="$([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) == '.NETFramework'">4.0.5.0</AssemblyVersion>
+    <AssemblyVersion Condition="'$(IsPackable)' == 'true' and $([MSBuild]::GetTargetFrameworkIdentifier('$(TargetFramework)')) == '.NETFramework'">4.0.6.0</AssemblyVersion>
+    <PackageValidationBaselineVersion>4.6.1</PackageValidationBaselineVersion>
+  </PropertyGroup>
+
+</Project>