Bump Polyfill from 3.0.0 to 4.0.0 in /src (#703)

Bumps [Polyfill](https://github.com/SimonCropp/Polyfill) from 3.0.0 to 4.0.0.
- [Commits](SimonCropp/Polyfill@3.0.0...4.0.0)

---
updated-dependencies:
- dependency-name: Polyfill
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

src/MarkdownSnippets/MarkdownSnippets.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="ProjectDefaults" Version="1.0.125" PrivateAssets="all" />
-    <PackageReference Include="Polyfill" Version="3.0.0" PrivateAssets="all" />
+    <PackageReference Include="Polyfill" Version="4.0.0" PrivateAssets="all" />
     <PackageReference Include="System.Memory" Version="4.5.5" Condition="'$(TargetFrameworkIdentifier)' == '.NETStandard' OR '$(TargetFrameworkIdentifier)' == '.NETFramework' OR '$(TargetFrameworkIdentifier)' == '.NETCOREAPP'" />
     <PackageReference Include="System.Net.Http" Version="4.3.4" Condition="'$(TargetFramework)' == 'net48'" />
   </ItemGroup>