[WIP] UAP_HAL_Linux: Basic safety switch infrastructure #35703

Job	Run time
build (base)	7m 0s
build (clang)	8m 5s
autotest (sitltest-rover)	16m 56s
autotest (sitltest-sailboat)	2m 38s
autotest (sitltest-balancebot)	7m 41s
	42m 20s

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