refactor: polish CoinJoin interface, use `WalletLoader` in Dash wallet initialization code, introduce new RPC `coinjoin status` #1827

Job	Run time
Build container / Build container	2m 17s
x86_64-pc-linux-gnu_nowallet / Build depends	58s
x86_64-pc-linux-gnu / Build depends	57s
arm-linux-gnueabihf / Build depends	1m 5s
x86_64-pc-linux-gnu_multiprocess / Build depends	1m 5s
x86_64-apple-darwin / Build depends	1m 10s
x86_64-w64-mingw32 / Build depends	57s
win64-build / Build source	23m 21s
linux64_fuzz-build / Build source	17m 19s
linux64-build / Build source	13m 44s
linux64_ubsan-build / Build source	23m 1s
linux64_sqlite-build / Build source	15m 5s
linux64_nowallet-build / Build source	13m 27s
linux64_multiprocess-build / Build source	47m 11s
linux64_tsan-build / Build source	23m 40s
arm-linux-build / Build source	15m 38s
mac-build / Build source	16m 45s
	3h 37m 40s

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