doxygen: reorganize directory structure #5359

Job	Run time
RT-Thread Online Packages (STM32F407 RT-Spark)	5m 5s
RTduino/Arduino Libraries (STM32F412 Nucleo)	12m 9s
RTduino/Arduino Libraries (Raspberry Pico)	10m 18s
others_at32_hc32_ht32	6m 30s
stm32l4_f0_f1	12m 38s
stm32_f2_f4	7m 18s
stm32_f7_g0_h7_mp15_u5_h5_wb5	4m 4s
nxp_renesas	4m 29s
nuvoton	3m 39s
gd32_n32_apm32	3m 34s
Infineon_TI_microchip	5m 2s
mips	1m 15s
aarch64	4m 7s
riscv-none	1m 36s
riscv64-unknown	2m 13s
hpmicro	1m 11s
llvm-arm	3m 50s
simulator	1m 2s
ESP32C3	22m 50s
i386-unknown	1m 6s
nordic(yml)	10m 29s
	2h 4m 25s

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