mavsdk_server: document and fixup C API #4410

Job	Run time
Coverage (ubuntu-22.04)	7m 20s
ubuntu-20.04 (mavsdk_server, superbuild)	17m 49s
ubuntu-22.04 (mavsdk_server, superbuild)	12m 29s
alpine 3.19.0 (musl)	10m 57s
ubuntu-20.04 (package, non-mavsdk_server)	12m 49s
ubuntu-24.04 (mavsdk_server, superbuild)	14m 5s
android-arm	6m 42s
ubuntu-22.04 (package, non-mavsdk_server)	11m 13s
ubuntu-24.04 (mavsdk_server, superbuild)	11m 50s
linux-armv6	6m 9s
android-arm64	6m 51s
ubuntu-24.04 (package, non-mavsdk_server)	10m 30s
ubuntu-24.04 (mavsdk_server, superbuild)	11m 42s
linux-armv7	5m 48s
android-x86	6m 36s
linux-arm64	5m 58s
android-x86_64	7m 2s
linux-arm64-lts	5m 31s
ios	55m 48s
linux-armv6-musl	12m 38s
macOS x64	13m 0s
ios_simulator_x64	6m 20s
macOS arm64	4m 56s
ubuntu-24.04 (style and proto check)	1m 41s
ios_simulator_arm64	59m 55s
linux-armv7l-musl	12m 23s
macOS framework x64	11m 13s
linux-arm64-musl	13m 27s
macOS framework arm64	4m 47s
ubuntu-20.04 (non-mavsdk_server, non-superbuild)	8m 25s
ubuntu-20.04 (non-mavsdk_server, hunter)	4m 58s
ubuntu-22.04 (non-mavsdk_server, non-superbuild)	6m 49s
ubuntu-22.04 (non-mavsdk_server, hunter)	4m 25s
Windows	13m 27s
ubuntu-24.04 (non-mavsdk_server, non-superbuild)	6m 39s
ubuntu-24.04 (non-mavsdk_server, hunter)	4m 15s
iOS XCFramework	0s
	6h 56m 27s

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