feat: add MIDI 2.0 Host class driver (USB-MIDI 2.0)

Add native USB-MIDI 2.0 Host class driver to TinyUSB. Implements
reactive architecture: enumerate, detect MIDI 2.0 capability, inform
application via callbacks.

Driver features:
- Parse both Alt Setting 0 (MIDI 1.0) and Alt Setting 1 (UMP)
- Detect bcdMSC version from descriptor
- Auto-select highest protocol (Alt 1 preferred if available)
- UMP read/write via endpoint streams
- Proper Audio Control interface skip (loop-based, following
  midi_host.c pattern)
- Endpoint open with tuh_edpt_open/tu_edpt_stream_open/clear
- usbh_driver_set_config_complete for USBH state machine
- Handle Audio Control itf_num in set_config gracefully
- 5 weak callback stubs (descriptor, mount, unmount, rx, tx)

Build system:
- Register midih2_* in usbh.c driver table
- Add midi2_host.h include to tusb.h
- Add CFG_TUH_MIDI2_LOG_LEVEL to tusb_option.h

All changes guarded by #if CFG_TUH_MIDI2 (default 0). Zero impact on
existing drivers and examples.

Tested: Waveshare RP2350-USB-A (Host) receiving UMP from Raspberry Pi
Pico (Device) via PIO-USB, board-to-board

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