[Azure Functions] Restore files moved by in-process Azure Functions SDK (#7419)

## Summary of changes

Improve support for in-process Azure Functions my restoring the files
moved by the SDK.

## Reason for change

The Azure Functions SDK for in-process functions moves files from
`$(PublishDir)**\*.dll` to `$(PublishDir)bin\` (keeping the directory
structure). This breaks the tracer because the files are not found where
expected. Furthermore, it splits the tracer files into two paths because
it moves only our `.dll` files but not other files, like `.so`,
`loader.confg`, or the agent binaries.

See
https://github.com/Azure/azure-functions-vs-build-sdk/blob/7a3e505c2382ee9c461985baef1603e980740ca6/src/Microsoft.NET.Sdk.Functions.MSBuild/Targets/Microsoft.NET.Sdk.Functions.Publish.targets#L134-L154

## Implementation details

Add a build target that runs after the SDK's
`_GenerateFunctionsAndCopyContentFiles` target. This new target moves
any files in `$(PublishDir)bin\datadog\**\*.dll` back to
`$(PublishDir)datadog\`, maintaining the directory structure.

Directory tree before:
```
.\publish\
├── bin
│   ├── datadog                                <---- dlls moved to bin/datadog/
│   │   ├── net6.0
│   │   │   └── Datadog.Trace.dll
│   │   ├── win-x64
│   │   │   ├── Datadog.Trace.ClrProfiler.Native.dll
│   │   │   └── Datadog.Tracer.Native.dll
│   │   └── win-x86
│   │       ├── Datadog.Trace.ClrProfiler.Native.dll
│   │       └── Datadog.Tracer.Native.dll
│   ├── (application files)
│   └── ...
├── datadog                                    <---- other tracer files stay in datadog/
│   ├── bin
│   │   ├── linux-amd64
│   │   │   └── datadog-serverless-compat
│   │   └── windows-amd64
│   │       └── datadog-serverless-compat.exe
│   ├── linux-x64
│   │   ├── Datadog.Trace.ClrProfiler.Native.so
│   │   ├── Datadog.Tracer.Native.so
│   │   └── loader.conf
│   ├── net6.0
│   ├── win-x64
│   │   └── loader.conf
│   └── win-x86
│       └── loader.conf
├── <function name>
│   └── function.json
├── <function name>
│   └── function.json
├── ...
│   └── function.json
└── host.json
```

Directory tree after:
```
.\publish\
├── bin
│   ├── (application files)
│   └── ...
├── datadog                                    <---- all tracer files stay in datadog/
│   ├── bin
│   │   ├── linux-amd64
│   │   │   └── datadog-serverless-compat
│   │   └── windows-amd64
│   │       └── datadog-serverless-compat.exe
│   ├── linux-x64
│   │   ├── Datadog.Trace.ClrProfiler.Native.so
│   │   ├── Datadog.Tracer.Native.so
│   │   └── loader.conf
│   ├── net6.0
│   │   └── Datadog.Trace.dll
│   ├── win-x64
│   │   ├── Datadog.Trace.ClrProfiler.Native.dll
│   │   ├── Datadog.Tracer.Native.dll
│   │   └── loader.conf
│   └── win-x86
│       ├── Datadog.Trace.ClrProfiler.Native.dll
│       ├── Datadog.Tracer.Native.dll
│       └── loader.conf
├── <function name>
│   └── function.json
├── <function name>
│   └── function.json
├── ...
│   └── function.json
└── host.json
```

## Test coverage

Tested manually. Will add automated tests before officially supporting
in-process Azure Functions.

## Other details
Fixes APMSVLS-136


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---------

Co-authored-by: Copilot <[email protected]>

Author: lucaspimentel

tracer/src/Datadog.AzureFunctions/Datadog.AzureFunctions.csproj

@@ -58,6 +58,9 @@
       <PackageCopyToOutput>false</PackageCopyToOutput>
     </None>
 
+    <None Include="Datadog.AzureFunctions.props" Pack="true" PackagePath="buildTransitive\Datadog.AzureFunctions.props" />
+    <None Include="Datadog.AzureFunctions.targets" Pack="true" PackagePath="buildTransitive\Datadog.AzureFunctions.targets" />
+
     <!-- win-x64 and win-x86 exclusions -->
     <None Remove="$(SourcePath)/win-*/Datadog.Profiler.Native.dll" />
     <None Remove="$(SourcePath)/win-*/datadog_profiling_ffi.dll" />

tracer/src/Datadog.AzureFunctions/Datadog.AzureFunctions.props

@@ -0,0 +1,6 @@
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <PropertyGroup>
+    <!-- Allow opting out of fix for in-process Azure Functions -->
+    <RestoreDatadogFiles Condition="'$(RestoreDatadogFiles)' == ''">true</RestoreDatadogFiles>
+  </PropertyGroup>
+</Project>

tracer/src/Datadog.AzureFunctions/Datadog.AzureFunctions.targets

@@ -0,0 +1,22 @@
+<!-- This build step is a workaround for the Azure Functions SDK moving our *.dll files from datadog/ to bin/datadog/
+     See https://github.com/Azure/azure-functions-vs-build-sdk/blob/7a3e505c2382ee9c461985baef1603e980740ca6/src/Microsoft.NET.Sdk.Functions.MSBuild/Targets/Microsoft.NET.Sdk.Functions.Publish.targets#L134-L154 -->
+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Target Name="_RestoreDatadogFiles"
+          AfterTargets="_GenerateFunctionsAndCopyContentFiles"
+          BeforeTargets="_FunctionsPostPublish"
+          Condition="'$(RestoreDatadogFiles)' == 'true'">
+    <!-- get a list of files that were moved -->
+    <ItemGroup>
+      <DatadogFilesAfter Include="$(PublishDir)bin\datadog\**\*.dll"/>
+    </ItemGroup>
+
+    <!-- move the files back -->
+    <Move SourceFiles="@(DatadogFilesAfter)"
+          DestinationFiles="$(PublishDir)datadog\%(RecursiveDir)%(Filename)%(Extension)"
+          OverwriteReadOnlyFiles="true" />
+
+    <RemoveDir Directories="$(PublishDir)bin\datadog"/>
+
+    <Message Text="[Datadog.AzureFunctions] Restored Datadog files from &quot;$(PublishDir)bin/datadog/&quot; back to &quot;$(PublishDir)datadog/&quot;" />
+  </Target>
+</Project>