Public C++ library API for symbolizing/deobfuscating traces

### Feature request

The `traceconv bundle` command does an opaque "take a trace, produce an
enriched trace" operation: it symbolizes native frames, applies ProGuard/R8
deobfuscation, and emits a TAR containing the enriched output.

The implementation already exists as a C++ entry point
(`TraceToBundle()` in `src/traceconv/trace_to_bundle.h`, with `EnrichTrace()`
in `src/trace_processor/util/trace_enrichment/trace_enrichment.h` doing the
actual work), but it lives under `src/` and is not part of the public API.

### What we'd like

An `include/` C++ API that takes:

- A path to (or bytes of) an input trace.
- A `BundleContext`-equivalent (explicit symbol paths, ProGuard mapping
specs, flags).

...and returns the enriched trace opaquely — without the caller having to
instantiate a `TraceProcessor`, execute queries, or know anything about
`TracePacket` internals.

If you hit this, please +1 so we can prioritise.

Start with src/traceconv/trace_to_bundle.h and the TraceToBundle() entry point, then read src/trace_processor/util/trace_enrichment/trace_enrichment.h and EnrichTrace(). Define how an include/ API should accept paths or bytes plus BundleContext-equivalent settings and return enriched output opaquely. Done means a public C++ interface exists without requiring callers to instantiate TraceProcessor, run queries, or know TracePacket internals.

Written by the indexing model from the issue text.