Perf: ~250ms spent in __objc_load_compiled_modules during initial IslandwoodNews launch on phone

[jaredhms]

Investigate why we're spending ~250+ ms loading binaries while launching IslandwoodNews before we even get a UIThread.

[DHowett-MSFT]

It would be very cool to add TraceLogging or ETL to libobjc2.

If we:

1. Move the two resolve/load loops into libobjc2.
2. Fold them together.
3. Perhaps pass an HMODULE instead of a bucket of pointers.
4. Add TraceLogging.

We could get:

• Fine-grained per-module class-level performance metrics.
• An understanding of which frameworks are spending a long time in +load.

The major culprit here is likely to be +load methods.

[davidchisnall]

In the upstream x86-64 objc_msgSend implementation, we have support for tracing entry to and exit from methods invoked via the objc_msgSend family. This comes with around a 10-20% performance hit on message sending benchmarks, so it's not enabled by default.