Fix method signature for memmove and memset in SpanHelpers.ByteMemOps

[kotlarmilos]

Description

This PR fixes modifiers order encountered when building mono runtime.

src/libraries/System.Private.CoreLib/src/System/SpanHelpers.ByteMemOps.cs(259,9): error IDE0036: Modifiers are not ordered (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0036) [/Users/miloskotlar/dotnet/runtime-ios/src/mono/System.Private.CoreLib/System.Private.CoreLib.csproj]
src/libraries/System.Private.CoreLib/src/System/SpanHelpers.ByteMemOps.cs(482,9): error IDE0036: Modifiers are not ordered (https://learn.microsoft.com/dotnet/fundamentals/code-analysis/style-rules/ide0036) [/Users/miloskotlar/dotnet/runtime-ios/src/mono/System.Private.CoreLib/System.Private.CoreLib.csproj]

Introduced in #122791

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[Copilot]

Pull request overview

This PR fixes modifier ordering issues in two method declarations that were causing build errors when building the Mono runtime. The changes ensure compliance with the C# modifier ordering rules specified in .editorconfig.

• Reorders modifiers from private static unsafe extern to private static extern unsafe for two internal methods
• Resolves IDE0036 compiler errors that were blocking Mono builds

[jkotas]

I am wondering why this was not caught by CI. Do you happen to know? It is not the first time something like this happened, but I was not able to figure out how it sneaked through.

[kotlarmilos]

I was building runtime packs using the following command:

./build.sh --restore --build --pack --configuration Release /p:TargetRid=ios-arm64 --arch arm64 --os ios /p:DotNetBuildAllRuntimePacks=true

I see that the ios packs were built on the PR. I will check if there is any difference when DotNetBuildAllRuntimePacks is passed.