New function to get itfnum from HID instance #108

Job	Run time
build-board (device/audio_test device/board_test device/cdc_dual_ports device/cdc_msc)	23s
build-arm (broadcom_32bit)	34s
build-board (device/cdc_msc_freertos device/dfu_runtime device/hid_composite device/hid_composite...	26s
build-arm (imxrt)	3m 34s
unit-test	36s
build-board (device/hid_generic_inout device/hid_multiple_interface device/midi_test device/msc_d...	2m 57s
build-arm (lpc15)	53s
build-board (device/net_lwip_webserver)	17s
build-arm (lpc18)	1m 10s
build-board (device/uac2_headset device/usbtmc device/webusb_serial host/cdc_msc_hid)	16s
build-arm (lpc54)	1m 29s
build-arm (lpc55)	2m 25s
build-arm (mm32)	58s
build-arm (msp432e4)	1m 3s
build-arm (nrf)	4m 41s
build-arm (rp2040)	41m 27s
build-arm (samd11)	1m 44s
build-arm (samd21)	9m 26s
build-arm (samd51)	10m 8s
build-arm (saml2x)	7m 6s
build-arm (stm32f0)	1m 53s
build-arm (stm32f1)	1m 20s
build-arm (stm32f4)	4m 21s
build-arm (stm32f7)	3m 20s
build-arm (stm32h7)	2m 48s
build-arm (stm32l4)	2m 14s
build-arm (tm4c123)	48s
build-arm (xmc4000)	55s
	1h 49m 12s

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