Remove obsolete System.AndroidPlatform methods and native implementations

[Copilot]

This PR removes obsolete managed code that references System.AndroidPlatform, which was part of the Mono Android runtime but was never used in modern .NET. The issue was identified by @filipnavara and confirmed safe to remove by @jonathanpeppers after verifying that these APIs don't exist in dotnet/runtime.

Changes Made

Removed Methods from AndroidEnvironment.cs:

• GetDisplayDPI() - Previously called by System.Drawing.GraphicsAndroid.FromAndroidSurface() (already marked as obsolete for android31.0)
• GetDefaultTimeZone() - Previously called by System.Core!System.AndroidPlatform.GetDefaultTimeZone()
• GetDefaultSyncContext() - Previously called by mscorlib.dll!System.AndroidPlatform.GetDefaultSyncContext()
• GetInterfaceAddresses() - Previously called by System.dll!System.AndroidPlatform.getifaddrs
• FreeInterfaceAddresses() - Previously called by System.dll!System.AndroidPlatform.freeifaddrs
• GetDefaultProxy() - Previously called by System.dll!System.AndroidPlatform.GetDefaultProxy()

Additional Cleanup:

• Removed the _Proxy class that was only used by GetDefaultProxy()
• Removed unused P/Invoke declarations from RuntimeNativeMethods.cs:
  • _monodroid_timezone_get_default_id()
  • _monodroid_getifaddrs()
  • _monodroid_freeifaddrs()

Native Code Cleanup:

• Removed P/Invoke method entries from both CLR and Mono P/Invoke table generators
• Regenerated P/Invoke tables using generate-pinvoke-tables.sh
• Removed unused native C++ implementations:
  • _monodroid_timezone_get_default_id() functions (CLR & Mono)
  • Complete xamarin_getifaddrs.cc files and header (CLR & Mono - 2,200+ lines)
  • Updated CMakeLists.txt files to remove build references
• Fixed linker error by removing obsolete symbols from Mono version script

Impact

This is a breaking change that removes internal APIs that were never intended for public use in modern .NET for Android. No external code should be affected as these were internal implementation details for obsolete System.AndroidPlatform methods.

Total lines removed: 2,456 lines across 16 files
Build status: ✅ Successful with no new warnings or errors

Fixes #10381.

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[jonathanpeppers]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jonathanpeppers]

@copilot check my review comments

[jonathanpeppers]

@copilot there is a new error:

(_BuildAndroidRuntimes target) -> 
         ld.lld : error : version script assignment of 'LIBMONO_ANDROID' to symbol '_monodroid_freeifaddrs' failed: symbol not defined [/Users/builder/azdo/_work/4/s/android/src/native/native-mono.csproj]
         ld.lld : error : version script assignment of 'LIBMONO_ANDROID' to symbol '_monodroid_getifaddrs' failed: symbol not defined [/Users/builder/azdo/_work/4/s/android/src/native/native-mono.csproj]
         clang++ : error : linker command failed with exit code 1 (use -v to see invocation)

Is something using these methods? or is there another file to update?

[Copilot]

@copilot there is a new error:

(_BuildAndroidRuntimes target) -> 

...

The error was caused by the Mono version script file still referencing the removed symbols. I've fixed it by removing _monodroid_freeifaddrs and _monodroid_getifaddrs from src/native/mono/libmono-android.map.txt. The CLR version was unaffected since it didn't have these symbols in its version script. Fix in commit a6a34d5.

[filipnavara]

LGTM (if the build passes)

[jonathanpeppers]

@copilot there are a few minor formatting issues

[Copilot]

@copilot there are a few minor formatting issues

Fixed all formatting issues in commit 0dc673c - removed unnecessary blank lines from the three affected files.

[grendello]

I would hold off with this PR until we branch for .NET10 release. The Mono changes can potentially be breaking ones, especially removal of the *ifaddr p/invokes. There's a slim but non-zero chance that some app out there is using any of those APIs.

[filipnavara]

I find it very unlikely that any app would depend on it. This was internal implementation detail that has not been used since .NET 5 (unified .NET always shipped the shims in their native libraries).

The reason I found this in the first place is that I looked into reusing the native code for CoreCLR GC bridge for NativeAOT (which now has the same API). I was very surprised to find that this is still lurking around and that it was even ported to CoreCLR host code base.

(in fact, I would argue that from security perspective it's safer to ship less dead code in a LTS release; well, even if LTS is irrelevant for the mobile workloads)

[jonathanpeppers]

main is basically .NET 10 RC 1, given it is deleting 2,400 lines. I'm ok to defer to @grendello's suggestion. We can wait to merge until we've branched for .NET 10 to put this in .NET 11. If we were on earlier previews, I would say just merge it.

It must not affect app size too much, as we have tests that fail if file sizes change within a certain percentage.

[dartasen]

There's a slim but non-zero chance that some app out there is using any of those APIs.

Isn't it internal APIs ?