[lib][heap] add a command to toggle heap tracing
[lib][heap] add a command to toggle heap tracing

The code is only built on debug builds.

srodrig1/lk,srodrig1/lk,hollanderic/lkstuff,littlekernel/lk,minglun-tsai/lk,srodrig1/lk,travisg/lk,minglun-tsai/lk,sndnvaps/lk,travisg/lk,srodrig1/lk,ErikCorryGoogle/lk,travisg/lk,sndnvaps/lk,littlekernel/lk,minglun-tsai/lk,hollanderic/lkstuff,ErikCorryGoogle/lk,minglun-tsai/lk,hollanderic/lkstuff,littlekernel/lk,srodrig1/lk,sndnvaps/lk,littlekernel/lk,ErikCorryGoogle/lk,hollanderic/lkstuff,travisg/lk,sndnvaps/lk,sndnvaps/lk,ErikCorryGoogle/lk