Warn when Android full trimming strips the debug IDs needed for symbolication

## Problem

Android apps that trim their own assemblies (`TrimMode=full`, e.g. `AndroidLinkMode=Full`) get no symbolication for managed stack traces in Release builds, and nothing tells the user why.

In Release the Android SDK forces `TrimmerRemoveSymbols=true` in its `_PrepareLinking` target unless `AndroidIncludeDebugSymbols=true` ([`Microsoft.Android.Sdk.TypeMap.LlvmIr.targets`](https://github.com/dotnet/android/blob/main/src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.TypeMap.LlvmIr.targets); the same override has existed since .NET 6). With full trimming, ILLink rewrites the app's assemblies and drops their debug directory, so:

- `obj/.../linked/.dll` has an all-zero debug ID and no `linked/*.pdb` is produced
- at runtime the SDK logs `Skipping debug image for module '.dll' because the Debug ID couldn't be determined`
- events have no `debug_meta` image for the app assembly, so frames can't be symbolicated even though the build uploaded PDBs

With the default `TrimMode=partial`, app assemblies are copied through untouched, keep their debug IDs, and symbolication works.

Found while verifying .NET 11 assembly store support end to end (#5577) with `Sentry.Samples.Android`, which sets `AndroidLinkMode=full`.

## Workaround (verified)

Setting `TrimmerRemoveSymbols=false` as a normal csproj property (or `-p:`) does **not** work — `_PrepareLinking` overrides it. It has to be set after that target runs:

```xml

false

```

With that, and `AndroidLinkMode=full` unchanged, on `net11.0-android37.0` / arm64: ILLink emits `linked/*.pdb`, the trimmed DLL and its PDB share a real debug ID, `Sentry.targets` already uploads `linked/*.pdb`, and the captured event carries the `pe_dotnet` debug image with a symbolicatable frame.

Caveats: `_PrepareLinking` is a private Android SDK target, so this could break in a future workload. `AndroidIncludeDebugSymbols=true` also keeps symbols but changes other Release behaviour (type map kind, CoreCLR native library exclusions, Mono debugger component), so it isn't a good general recommendation. The cost of keeping symbols in the APK is negligible — PDBs aren't packaged, only each assembly's debug directory is retained.

## Proposal

We shouldn't flip the property for users (they may want symbols removed), but we should make the consequence visible:

1. **Build warning** from `Sentry.targets` for Android apps when app assemblies are trimmed (`TrimMode=full`) and `TrimmerRemoveSymbols` is `true` at link time, explaining that managed stack traces won't symbolicate and pointing to the docs. It can't distinguish an intentional `true` from the Android SDK's forced value, so it should be informational and suppressible via `NoWarn`. Don't warn for `TrimMode=partial`.
2. **Troubleshooting docs**: add an Android section to the .NET troubleshooting page (`docs/platforms/dotnet/common/troubleshooting.mdx` in sentry-docs), alongside the existing "Stack traces are not symbolicated on iOS, macOS and Mac Catalyst" section, covering the cause, the workaround above and its caveats. The "Missing or Unhelpful Stack Traces in AOT Compiled Apps" section is about the stack trace factory, which is a different cause.

Read Sentry.targets and the linked Microsoft.Android.Sdk.TypeMap.LlvmIr.targets _PrepareLinking entry point, then run the net11.0-android37.0 arm64 full-trim scenario described in the issue. Done means an informational, suppressible warning appears only for full trimming with symbols removed, and docs/platforms/dotnet/common/troubleshooting.mdx documents the cause, workaround, and caveats.

Written by the indexing model from the issue text.