[native] Replace the AndroidSystem path statics with a POD buffer - #12552

…12571)

Part of #12533: remove the remaining allocating C++ library types from the CoreCLR assembly store and its decompressed-assembly cache.

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All prerequisites (#12541, #12545, #12551, #12552, #12560, #12568, and #12570) have merged. This branch was rebuilt on `main` at `4b0cc8efa9`. The runtime changes are confined to `src/native/clr/host/assembly-store.cc`, with cache regression coverage and APK size baseline updates alongside them. The already-merged startup, timing, DSO-loader, and other prerequisite changes are no longer included in this PR's diff. Upstream's pthread-backed `lock_guard` is preserved.
<!-- /stack-prerequisites -->

### Changes

- Replace `std::deque<WriteRequest>` with an intrusive FIFO linked through `WriteRequest::next`.
- Replace the queued request's `std::unique_ptr<uint8_t[]>` with an explicit `uint8_t *payload`. Allocate the request and payload separately with two `malloc` calls and release both with two `free` calls on every completed or discarded write. If payload allocation fails, release the request and skip the write. No trailing-storage pointer arithmetic or explicit over-alignment is needed.
- Replace the cache directory and per-request `std::string` paths with a process-lifetime directory string and checked `snprintf` formatting. Requests store the descriptor index instead of a path; the writer reconstructs the destination from the immutable cache directory. Replace temporary-file name construction and matching with `snprintf` and `strstr`.
- Use a scoped `CachePath` buffer for directory creation, reads, writes, and stale-file cleanup. Short paths remain on the stack; longer paths retry in an exactly sized `malloc` allocation that is freed on every exit. Formatting and allocation failures are logged and remain non-fatal for the optional cache, unlike the abort-on-failure `Util::format_with_retry` helper.
- Allocate the decompression tracking array and assembly-name table with `calloc`, replacing their `unique_ptr`/`new[]` allocations.
- Extend the existing device cache regression test with a Java Application that supplies a code-cache directory longer than 1 KB. Cover persistence, mapping, corruption recovery, and stale temporary-file cleanup for both ordinary and long paths.

The asynchronous writer, queue byte limit, cache footer validation, and scope-based pthread locking are retained. `Util::LocalPathBufferSize` is the stack fast-path size, not a hard path limit; truncated paths are never used for I/O. The change does not alter linker flags or other runtime hosts.

### Original measurements

These results were recorded on the original pre-rebuild branch, **not on the current revision**:

| Release, arm64 | Before | After |
|---|---:|---:|
| Undefined libc++ references in `assembly-store.cc.o` | 12 | 0 |
| Undefined libc++ references across the CoreCLR host | 12 | 0 |
| `libnet-android.release.so` size | 520,112 bytes | 203,776 bytes |

Reaching zero references allowed the linker to stop pulling members from `libc++_static.a`. Relinking without libc++ also succeeded on that original branch; dropping the linker flag remains a follow-up.

### Current validation status

The malloc fallback passed sanitizer-backed host cases covering stack/heap boundaries, nested lifetimes, allocation failure, and formatting/retry failures. The cache namespace extracted unchanged from the current source, using the real CRC32 and mutex helpers with runtime configuration/property stubs, compiled with the Android NDK for arm64, arm32, and x86_64. A standalone arm64 emulator harness passed cache initialization, asynchronous persistence, mmap reads, corruption recovery, and stale-file cleanup with both short and greater-than-1-KB paths. The generated Java regression-test application also compiled against the Android API. `git diff --check` passes.

A local `dotnet build src/native/native-clr.csproj` restored packages but could not reach native compilation because this worktree lacks `xa-prep-tasks.dll` and `Xamarin.Android.Tools.BootstrapTasks.dll`. The complete native host build and repository device regression suite have **not** been run for this revision; the locally built SDK is unavailable. Binary measurements have not been repeated. The original branch's reported full native builds and binary measurements remain historical, not validation of this revision.