Track transition from launch dyld to shared-cache dyld

On macOS, a process will be launched with /usr/lib/dyld (the
dynamic linker) and the main binary by the kernel.  The
first thing the standalone dyld will do is call into the dyld
in the shared cache image.  This patch tracks the transition
between the dyld's at the very beginning of process startup.

In DynamicLoaderMacOS::NotifyBreakpointHit() there are two new
cases handled:

`dyld_image_dyld_moved` which is the launch /usr/lib/dyld indicating
that it is about call into the shared cache dyld ane evict itself.
lldb will remove the notification breakpoint it set, clear the binary
image list entirely, get the notification function pointer value out
of the dyld_all_image_infos struct (which is the notification fptr
in the to-be-run shared-cache dyld) and put an address breakpoint
there.

`dyld_notify_adding` is then called by shared-cache dyld, and we
detect this case by noticing that we have an empty binary image list,
normally impossibe, and treating this as if we'd just started a
process attach/launch.

Differential Revision: https://reviews.llvm.org/D127247
rdar://84222158