Piano+LibDSP: Move Track to LibDSP

This is a tangly commit and it fixes all the bugs that a plain move
would have caused (i.e. we need to touch other logic which had wrong
assumptions).

Userland/Libraries/LibDSP/CMakeLists.txt

@@ -1,9 +1,9 @@
 set(SOURCES
     Clip.cpp
-    Track.cpp
     Effects.cpp
     Synthesizers.cpp
     Keyboard.cpp
+    Track.cpp
 )
 
 serenity_lib(LibDSP dsp)