* Prefer `PROJECT_{SOURCE,BINARY}_DIR` to `CMAKE_` ones
* Extend use of 3rd-party dir vars to reduce duplication
* Fix typo in submodule repo name
* Remove `CURL::libcurl` target fallback
The target is always available since CMake 3.12, which is our current
minimum version.
* Use imported CMake target for CURL
* Use imported CMake target for fmtlib
* Use imported CMake target for WideInteger
* Use imported CMake target for FastFloat
* Use imported CMake target for UtfCpp
* Use imported CMake target for Threads
* Use imported CMake target for Iconv
* Use imported CMake target for crypto backend
* Use imported CMake target for GTK
* Use imported CMake target for Qt
* Use imported CMake target for deflate
* Use imported CMake target for libevent
* Use imported CMake target for natpmp
* Use imported CMake target for miniupnpc
* Use imported CMake target for dht
* Use imported CMake target for psl
* Use imported CMake target for libutp
* Use imported CMake target for libb64
* Use include directories from libtransmission target