[NativeAOT] Add printf gref logging

[jonathanpeppers]

Dependency

Depends on #12211 and targets its jonathanpeppers-finish-gc-bridge-printf branch.

Part of #12139.

Design

Adds a non-exported printf-style OSBridge::_monodroid_gref_logf() path for the shared CoreCLR/NativeAOT GC bridge. It formats directly to logcat with log_writev() and to the gref file with vfprintf(), using va_copy() so both sinks can consume the arguments without allocating or transferring ownership.

The existing exported _monodroid_gref_log(const char*) entry point, P/Invoke registration, managed callers, and MonoVM implementation remain unchanged.

Scope

Migrates only the three intentionally deferred std::format calls in src/native/clr/host/bridge-processing.cc that feed the gref file/logcat pipeline.

Behavior preservation

• Retains the existing Logger::gref_log(), Logger::gref_to_logcat(), LOG_GREF, and gc_spew_enabled() gates and surrounding control flow.
• Preserves message text, punctuation, newlines, source locations, and sink flushing.
• Uses explicit 0x prefixes with PRIxPTR/uintptr_t so handles retain lowercase pointer-width hexadecimal output, including 0x0 for null handles.
• Keeps the existing null-message handling on the exported string API; the new internal format argument is also null-safe.
• Borrows format strings and arguments only for the duration of the call and introduces no returned or transferred ownership.

Non-goals

• Does not change the managed/native ABI or add a new P/Invoke symbol.
• Does not modify MonoVM-only gref logging.
• Does not migrate unrelated formatting outside the NativeAOT-reachable shared GC bridge.

Validation

Prerequisites initialized in the fresh worktree:

• dotnet build build-tools\xa-prep-tasks\xa-prep-tasks.csproj -v:minimal
• dotnet build build-tools\Xamarin.Android.Tools.BootstrapTasks\Xamarin.Android.Tools.BootstrapTasks.csproj -v:minimal
• git submodule update --init -- external/libunwind

Validation run:

• dotnet build src\native\native-nativeaot.csproj -p:AndroidSupportedTargetJitAbis=arm64-v8a -p:AndroidSupportedTargetAotAbis=arm64 -v:minimal
• dotnet build src\native\native-clr.csproj -p:AndroidSupportedTargetJitAbis=arm64-v8a -p:AndroidSupportedTargetAotAbis=arm64 -v:minimal
• rg "std::format" src\native\clr\host\bridge-processing.cc (no matches)
• git diff --check

No focused existing test target covers this internal OSBridge formatting boundary.

[Copilot]

Pull request overview

Adds an internal printf-style gref logging helper for the shared CoreCLR/NativeAOT GC bridge, and migrates the remaining std::format-based gref messages in bridge-processing.cc to avoid libc++ formatting dependencies while preserving existing gref logging behavior.

Changes:

• Introduce OSBridge::gref_logf(const char* format, ...) which logs to logcat via log_writev() and to the gref file via vfprintf(), using va_copy() for dual-sink consumption.
• Replace three std::format call sites in src/native/clr/host/bridge-processing.cc with gref_logf() and PRIxPTR-based pointer formatting.
• Add <cinttypes> include to support PRIxPTR.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/native/clr/include/host/os-bridge.hh	Declares new internal OSBridge::gref_logf() printf-style gref logging API.
src/native/clr/host/os-bridge.cc	Implements gref_logf() to write to logcat and the gref file without allocating intermediate strings.
src/native/clr/host/bridge-processing.cc	Migrates three gref log messages from std::format to gref_logf() with pointer-width hex output.